Indirect water heater questions and answers.

FAQs about indirect fired water heaters help diagnose and fix varous problems - helping you get more out of your hot water system.

In this article series we define and explain indirect-fired hot water heaters, describing the characteristics & advantages of this method for making domestic hot water where a gas or oil fired heating boiler is installed.

Indirect-fired Water Heater FAQs help fix problems or help get more hot water

These questions and answers about indirect water heaters were posted originally at INDIRECT FIRED WATER HEATERS - be sure to check the operation and troubleshooting advice given starting there.

Illustration: typical piping of an indirect water heater shows the two sets of piping at the heater: a loop from the heating boiler, operating as a separate "heating zone" heats a coil inside the tankless water heater. In turn that coil heats incoming cold domestic supply water to produce domestic hot water. Adapted from Techtanium® water heater IO manual cited here.

[Click to enlarge any image]

On 2021-04-10 - by (mod) -

@Mike,

Feel that boiler out-to-Amtrol pipe along its full length; is it hot all the way?

Do all of your heating zones work OK? If so (double check) and as there's just one circulator pump and we're using zone valves for zones, we pretty much rule out a bad circulator pump.

If not I suspect a blockage or even a leak from the heater coil (in the Amtrol WH7Z) into the Amtrol hot water tank itself .

How is the pipe routed? Could there be an air-blocakge?

On 2021-04-10 by Mike

I have a Amtrol WH7Z that will not produce hot water. My setup is the boilermate is running of its on zone value using the existing boilers circulating pump. My boiler is working fine and heats all the other zones in the house. When I turn the boilermate temp control to call for heat the boiler will fire and the pump is working fine. If I feel the boiler supply line it is very hot guessing around 150-180. When I feel the boiler return line its luke warm at best. I have let it run for hours and it will not produce any hot water. Also my setup does not have a mixing valve. Any suggestions would be greatly appreciated.

On 2020-10-18 - by (mod) -

Dave,

Have you tried setting down the temperature on the aquastat and circulator control that use hot water from the steam boiler to heat the water in the indirect-fired hot water tank?

You ought not need boiling water (making steam) to heat the indirect water heater, producing such hot water only when the building heating thermostats are calling for (steam) heat.

On 2020-10-18 by Dave

When my indirect water heater is heating up, the boiler is causing the radiators to get steam (closed- steam system). how do I control the temp so it is not heating up at 100 C?

On 2020-09-16 by Mike - John Wood indirect water heater, # JW5-40IT

I have a John Wood indirect water heater, # JW5-40IT, installed in 2007, that recently stopped working. It seemed that it just wasn't calling for the boiler to activate, so we looked to the thermostat. When the tank wires that connect to the thermostat were touched together (i.e. bypassing the thermostat), it would activate; so, I replaced the thermostat, and this seemed to work very briefly (like, only when first turned on, for about 15 min).

Then, it seemed like pushing the reset button would start it, but now when you push the reset, you can hear a few clicks and valves that seem to indicate that it is activating the boiler, but the boiler doesn't turn on and it goes quiet.

The boiler is working. There are 2 zones: one for the entire house heat, one for the water heater. I can get the water to heat up by turning on the house heat for ~ 20 min. Each zone is controlled by an Erie Pop Top valve actuator (and they are wired to each other); the one to the water heater was replaced at some point between '07 and now. I'm confused about the wiring here - it's not connected the way the diagrams I can find indicate it should be...but, it was installed originally, and replaced, by the plumber, and it's been working for 13 years.

When checking on the current problem, I found the water heater actuator to be very hot to the touch, even though the pipe below it was cold. I can make a diagram of the wiring here if it seems relevant. I'll say that, when investigating this, I found one loose wire here and thought I'd found the problem; I connected it where it looked like it came off...but I'm not 100% positive I got it right.

Thank you so much for any advice. I'm not an electrical expert but I have a multimeter and can do some basic checks myself. Happy to get a plumber (or electrician?), but I am generally a do-it-yourselfer when I can; also, I can't find a local plumber that anyone I know recommends!

On 2020-03-31 - by (mod) -

Blair:

The hot water pipes to the Superstor indirect water heater tell us that the boiler is trying to heat the water in the water tank. But if you are getting NO hot water in the home, do you mean no water flow or water flows but is cold? The potential causes are different.

If no water flow: find a closed valve or clogged hot water pipe or elbow.

If water flows but is not hot - if the water is tepid I suspect that the dip tube in the water heater has disintegrated



Anthony:

Yes, a leaking heat exchanging coil can cause a rise in boiler water pressure. That's because the building's water pressure (often 30-80 psi) is often well above the boiler's internal water pressure (12-30 psi)

Watch out: over pressure in the boiler will normally cause the relief valve to open and discharge or at least drip. Left un-attended the leaking temperature-pressure relief valve can become clogged with scale and debris, risking a serious BLEVE explosion at the boiler.

On 2020-03-31 by Blair

I have a old superstor tank model # SS-30 not getting any hot water anywhere in my house but the pipes going into the tank are hot. Tried turning up the dial to 150 hot just to see if the water would get warm but no luck any thoughts of what I should do ?

On 2020-03-14 by anthonybozz - Can a leaking coil in my Peerless PP-40 tank cause the boiler pressure to rise?

My system uses a separate zone to heat water in my Peerless PP-40 indirect hot water tank.

(1) Can a defective, water-logged, Amtrol ST-5 tank (see attached photo), which is installed on the tank's cold water inlet, cause the boiler pressure to rise from 15-psi to 30-psi? Or,

(2) Can a leaking coil in my Peerless PP-40 tank cause the boiler pressure to rise?

On 2019-10-27 by (mod) - My Techtanium indirect hot water heater stopped working all of a sudden.

Juan

To provide a detailed reply please find your question and our answer at

INDIRECT WATER HEATER REPAIR - take a look at the advice given there and don't hesitate to ask follow-up information and to post photos of your actual Techtanium indirect water heater, the piping between it and the boiler, and the boiler itself.

You can only post one photo per comment but of course you can post multiple comments; they'll appear online after moderator approval.

On 2019-10-26 by Juan Vazquez

My Techtanium indirect hot water heater stopped working all of a sudden. It's is 9 years old and the anode rods were changed I'm February of this year. What could be the problem

On 2019-10-27 by (mod) - how to winterize an indirect water heater

Laurie:

Watch out: what you describe may be unsafe; that is, if you drain the indirect water heater tank but leave its heating coil hooked up to the heating boiler and the boiler running, the tank may be damaged; I would not do that without first checking with the manufacturer.

On 2019-10-25 by Lauri

I am trying to winterize a house (for an extended period of no one being there) that has radiant floor heating with an indirect hot water tank.

When we leave, we turn off the well pump. Radiant heat system is closed loop and continues to operate with glycol mixture. I would like to drain the water in the pipes in the house to preclude damage in the event of a broken pipe.

However, that leaves the indirect hot water tank still hooked to the (operating) boiler. And presumably empty, since we would have drained the pipes in the house. Is that safe?

On 2019-09-18 by equinn

I have a problem of slow recovery on indirect water tank. Current setup has thermostat on water tank which turns circulator pump when water temp drops below 130. During heating season it works fine.

During summer boiler is always operating at low end of range. I want the boiler to be notified that the water tank needs help, raise boiler temp until water temp demand is satisfied, shortening recovery time. Is there an thermostat/aquastat that I can replace the current thermostat to allow both a 120v and 24v connection? If not, is there some type of device that can be placed inline between thermostat/cirulator that would allow for a 24v connection?

On 2019-01-25 by rsmith

Thanks again for all of your help! We're talking with the HW manufacturer now, and keeping a close eye on the boiler. No more overflow water, fortunately. Will let you know when we find out the cause!

On 2019-01-23 by (mod) - screaming hot water circulator pump

Watch out:Overflow from the boiler's temperature-relief valve is dangerous, indicating over temperature or over pressure (or a more-subtle cause like water hammer) - prolonged leakage can lead to TPR valve clogging and in the worst case a boiler explosion - search InspectApedia.com for BLEVE EXPLOSION to see details.

If this were my job, and with new circulator pump, no air in the system, proper temperatures, proper water velocity, proper aquastat settings (all of which I mentioned earlier)

if the new circulator is screaming in distress I'd be on the phone with the indirect water heater manufacturer to ask them if they have other clues about why the circulators are getting killed on this installation.

On 2019-01-23 Randall Smith

Thanks again for the continued help! This problem has been perplexing us for several days with a number of symptoms.

Day 1. Around 10:30am there was only enough hot water for a 6 min shower. About 10 minutes later, pump was making a mechanical screeching sound (grinding?), and we shut it off at the main boiler switch.

Repair took out a Taco circulator to the indirect water heater and installed a B&G, confessing that these circulators were new to him. It was a “eco” unit, and he set it at “3” just at the max of the eco settings.

It also was installed 90° off of the other Taco circulators, but was installed in the same flow direction as the other Taco units. It didn’t seem to require any lubrication as it was a self-contained unit and the repair person did not add any.

He also noted that the expansion tank seemed full, and he wondered if this was affecting the psi. He took the psi to 30 and then reduced to 15, and tried to bleed the expansion tank a bit, but that was unsuccessful. He contemplated replacing (it had been replaced in 2011, system is 1992), but agreed to monitor it when he returned for the annual spring cleaning.

About 2 hours later the pipes were rattling, and we turned the circulator from 3 to 4, which seemed to make the problem stop.

About 6 hours later, _all_ the pipes in the house were rattling, apparently so badly it loosened a nut on the new circulator, and there was now water on the floor. We tightened the nut on the top of the circulator, mopped up about 2 gallons of water and turned off the system.

Day 2. There was still limited hot water for a shower.

Repair person now said it was due to air in the lines and spent about 2 hours bleeding the lines of _all_ the circulators, not just the one to the water heater. He also noted that the expansion tank and the overflow value were located close to a bend in the pipes (the house was built and installed with approved plans, but apparently is too close to the bend?).

Note: there are 5 zones in the house—three thermostats, one to the water heater and one to a Modine space heater immediately adjacent to the boiler leftover before the basement was finished. Also he readjusted max temp to approx 200 (had been historically running about around 220) and reduced psi from 15 to 10. All seemed to be working fine at that point.

Day 3. We were monitoring the system for possible water leaks, temperature, noises, etc. nearly all day and night.

Around 3:00pm, we now heard a sound like the motor wasn’t turning over. It was flashing green 13 times (~7 sec) to half that length off. The product manual suggested that was a defective electronics board. We turned off the system again. Repair person put in a new B&G circulator, bled the lines, and made sure there was hot water coming out of the water heater.

However, he now was concerned that there was a blockage in the line to the water heater, causing more strain on the circulator. He took apart the flow control at the top of the water heater loop. He said it was not popping up and would need to be replaced, but since he did not have one on his truck, he put back the part in the open position cautioning us that the water may be hotter coming out than before.

He also speculated that the coils in the water heater might be clogged causing strain on the circulator and would need to be blasted out, but again, he did not have the tools to do that work then (Saturday).

Day 4 & 5. Hot water ok. Heat ok. No water in the boiler room. No noise.

Also repair person called with an astronomical quote to replace flow control. We did not go forward with repair because we are not certain this will actually solve the problem.

Day 6. Same as before, except we noticed about 1/2 gallon of water from the boiler overflow spigot. We dumped out the water and have been monitoring—no further water.

Day 7. After a shower, we started hearing low grade humming from 2 floors away.

The new circulator was whining, but still with a solid blue light indicating that it was operating normally, but the hot water pipes in and out of the water heater were cold to the touch. It didn’t sound good, and we didn’t want another circulator to die, so we shut off system, and started troubleshooting on our own.

We just turned on the system again after about 3 hours off. Initially the circulator started whining again, but we adjusted the pump flow up and down back to 6 where it was, and the noise went away. We will keep monitoring.

We have confirmed that the new circulator is compatible with the Taco SR503 power supply. We have already noted our water heater model. If it matters, our boiler is a Utica SF-4150WT.

Any further insight is welcomed!

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2019-01-23 by (mod) -

Yep, Clark Van Oyen's comments box code only permits one image per comment, but of course one can post multiple comments (and images at one per).

220F is too hot for a normal boiler and risks dumping at the TP Relief valve.

The best aquastat settings would be HI 200, LO 20 or more below the HI,

I might keep the DIFF circuit working and set DIFF to the max or 25. to keep heat in the boiler to speed response when the indirect heater ("zone") wants help from the boiler.

The indirect water heater runs as what looks to the boiler and aquastat as simply another heating zone.

Amtrol warns against scalding hazards and recommends a tempering valve.

If you give us the brand and model of your tempering valve we can be sure we've found the installation instructions and proper positioning information.

The sketch below is from the Amtrol Boiler Mate WH-series INSTALLATION MANUAL [PDF] https://inspectapedia.com/plumbing/Amtrol-Boiler-Mate-Installation-Manual.pdf AMTROL, 1400 Division Road, West Warwick, RI 02893 T: 401.884.6300 F: 401.885.2567 www.amtrol.com
IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2019-01-23 by Randall Smith

Thanks for the help! I've attached one image (can't seem to figure out how to do multiples) that shows the circulator, the water heater, and the pipes connecting them. The new circulator is a B&G Ecocirc 19-16 CCFXYZ. The other (older) circulators for the house heat are by Taco, model 007-F4.

The water heater, if it matters, is an Amtrol 'Boiler Mate' WH-7P (41 gallons). The operating temperature at the boiler is set at 190 now, had been 220. When doing the initial repair the plumber felt the ~200F+ & ~20psi was too high and reduced it to 190F max and 15psi. Not sure if this is related to our current problems.

IMAGE LOST by older version of Clark Van Oyen’s useful Comments code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2019-01-23 by (mod) -

Randall

Thanks for an interesting and also of course troubling question. One can but suspect that we have not gotten down to the root cause of the problem.

It would be helpful to have

- the brand and model of circulator pump installed

- photos of the circulator, heater, boiler, piping and controls between them

- the operating temperature at the boiler

It's not clear to me how an anti-scald valve (I think that's the device your plumber calls a control valve) would cause circulator pump failure. Hydronic heating circulator pumps are designed to handle boiler water at the temperatures that occur normally in the heating system - up to close to 200 degF.

There can be some subtle causes of circulator pump failure:

- mounting the pump askew in its bracket, stressing the pump drive shaft

- improper lubrication

- low voltage (motor may run hot)

- pump ran air-bound, due to excessive air in the system - see AIR-BOUND HEATING SYSTEMS https://inspectapedia.com/heat/Air_Bound_Heating_System.php

- pump installed backwards - pumping in the wrong direction; also it's best to put the pump on the return side of the heating loop where temperatures are lower and pump life is longer

- variable speed pump set to wrong speed - too slow (radiators or heating loop too cool, pump runs longer)

- improper pump control - pump runs continuously and is a model not rated for continuous operation

- (rare & subtle) - improper piping installation, burrs, bends, obstructing water flow and causing turbulence in the pump, similar to excessive velocity if pump speed is too high (on variable speed pumps)

- (rare) very corrosive or very hard water, including scale or debris that blocks or jams the impeller

- leaks left un-repaired

- defective motor (motor may run hot, vibrate excessively, be unusually noisy, fail to pump proper volume) - if the defect originated at the factory, replacing the pump with another made in the same batch at the same time may simply repeat the problem.

Details about diagnosing and repairing circulator pumps begin at

CIRCULATOR PUMPS & RELAYS https://inspectapedia.com/heat/Circulator_Pump_Repairs.php

Please also take a look there.

This might also be helpful:

WATTS HOT WATER CIRCULATOR DIAGNOSTIC MANUAL [PDF] (2007) at https://inspectapedia.com/plumbing/Watts-hot-water-circulator-pump-Diagnostic-Manual.pdf
Watts Premier, Inc., Phoenix, AZ 85027 Phone: 800-752-5582 www.wattspremier.com

On 2019-01-23 by Randall Smith

We had a circulator on our indirect HW heater die (loud noises) and replaced.

This had initial problems due to air in the pipes, but once fixed there was little/no hot water and within a day the new circulator died as well. Plumber suggested a control value that is supposed to control flow was broken and opened it fully, noting this would make the hot water very hot (adults only in house) and would need to be fixed properly soon. Now, however, we are hearing the new circulator struggle with loud humming noises. Any ideas? Many thanks!

On 2019-01-23 by (mod) - troubleshooting indirect water heater circulator pump failures

Yep, Clark Van Oyen's comments box code only permits one image per comment, but of course one can post multiple comments (and images at one per).

220F is too hot for a normal boiler and risks dumping at the TP Relief valve. Also, Amtrol warns against scalding hazards and recommends a tempering valve.

If you give us the brand and model of your tempering valve we can be sure we've found the installation instructions and proper positioning information.

The sketch above is adapted from

the Amtrol BoilerMate™ WH-series INSTALLATION MANUAL [PDF] (2012)

AMTROL, 1400 Division Road, West Warwick, RI 02893 T: 401.884.6300 F: 401.885.2567 www.amtrol.com

On 2019-01-23 by Randall Smith

Thanks for the help! I've attached one image (can't seem to figure out how to do multiples) that shows the circulator, the water heater, and the pipes connecting them.

The new circulator is a B&G Ecocirc 19-16 CCFXYZ. The other (older) circulators for the house heat are by Taco, model 007-F4.

The water heater, if it matters, is an Amtrol 'Boiler Mate' WH-7P (41 gallons).

The operating temperature at the boiler is set at 190 now, had been 220. When doing the initial repair the plumber felt the ~200F+ & ~20psi was too high and reduced it to 190F max and 15psi. Not sure if this is related to our current problems.

On 2019-01-23 by (mod) -

Randall

We have not gotten down to the root cause of the problem.

It would be helpful to have

- the brand and model of circulator pump installed

- photos of the circulator, heater, boiler, piping and controls between them

- the operating temperature at the boiler

It's not clear to me how an anti-scald valve (I think that's the device your plumber calls a control valve) would cause circulator pump failure. Hydronic heating circulator pumps are designed to handle boiler water at the temperatures that occur normally in the heating system - up to close to 200 degF.

There can be some subtle causes of circulator pump failure:

- mounting the pump askew in its bracket, stressing the pump drive shaft

- improper lubrication

- low voltage (motor may run hot)

- pump ran air-bound, due to excessive air in the system - see AIR-BOUND HEATING SYSTEMS https://inspectapedia.com/heat/Air_Bound_Heating_System.php

- pump installed backwards - pumping in the wrong direction; also it's best to put the pump on the return side of the heating loop where temperatures are lower and pump life is longer

- variable speed pump set to wrong speed - too slow (radiators or heating loop too cool, pump runs longer)

- improper pump control - pump runs continuously and is a model not rated for continuous operation

- (rare & subtle) - improper piping installation, burrs, bends, obstructing water flow and causing turbulence in the pump, similar to excessive velocity if pump speed is too high (on variable speed pumps)

- (rare) very corrosive or very hard water, including scale or debris that blocks or jams the impeller

- leaks left un-repaired

- defective motor (motor may run hot, vibrate excessively, be unusually noisy, fail to pump proper volume) - if the defect originated at the factory, replacing the pump with another made in the same batch at the same time may simply repeat the problem.

Details about diagnosing and repairing circulator pumps begin at

CIRCULATOR PUMPS & RELAYS where we expand our checlist of causes of hot water circulator pump failures

Please also take a look there.

This might also be helpful:

WATTS HOT WATER CIRCULATOR DIAGNOSTIC MANUAL [PDF] Watts Premier, Inc., Phoenix, AZ 85027 Phone: 800-752-5582 www.wattspremier.com

On 2019-01-23 by Randall Smith - circulator on indirect water heater died, replaced, sick again

We had a circulator on our indirect HW heater die (loud noises) and replaced. This had initial problems due to air in the pipes, but once fixed there was little/no hot water and within a day the new circulator died as well.

Plumber suggested a control value that is supposed to control flow was broken and opened it fully, noting this would make the hot water very hot (adults only in house) and would need to be fixed properly soon. Now, however, we are hearing the new circulator struggle with loud humming noises. Any ideas? Many thanks!

On 2019-01-16 by (mod) - indirect hot water tank leaks from the aquastat.

KS

A closer examination of your water heater is needed - perhaps you can post some photos here for comment.

I can imagine a failed gasket, loose connecting or mounting screws, or corrosion as causes for leaks.

On 2019-01-16 by kschenker2

I’m trying to figure out why my indirect hot water tank would leak from the aquastat. I noticed the other day a steady drip coming out of the nub that connects the aquastat to the tank where the copper wire runs into the inner part of the tank. Any ideas are appreciated!

On 2018-11-22 by Anonymous

Thank you

On 2018-11-22 by (mod) - ok then to shut off the circulation lines to the water maker?

You can do that but you may find that you need to sanitize the water heater when you are restoring it to service.

On 2018-11-21 by Anonymous

Would it be ok then to shut off the circulation lines to the water maker and the water supply to the water maker their by shutting off all hot water lines eliminating any linking possibility

On 2018-11-20 by (mod) -

It seems to me that you were just turn the temperature down on the thermostat control in your indirect water heater. You don't have to turn it off completely although you could, by turning off the circulator that feeds that heater. The reason I say you don't have to turn it off completely is because if you're not using water, the remaining standby losses are trivial

On 2018-11-19 by Anonymous

If you won’t to shut off you’re water maker while leaving heat on in the winter for a few months what do you do to isolitate the water maker

On 2018-04-23 by (mod) - burner is cycling on and off after a short while

Ian,

Since an indirect fired water heater (the subject of this page) has no burner of its own, I am guessing that you're describing a problem with your oil or gas fired heating boiler that supplies heat to your indirect water heater. Let's start by identifying the type of heating equipment: oil or gas or other fuel.

Try starting diagnostics at BOILERS, HEATING

Our illustration of a tankless water heater demonstrates how a mixing valve may be used to temper outgoing hot water to avoid scalding and also illustrates one (of several) version of the piping connections to an indirect water heater.

On 2018-04-23 by Ian

The burner is cycling on and off after a short while after a while the fan starts up ad normal. What is the cause

[Click to enlarge any image]

On 2018-02-26 by (mod) - plumbing for an HTP indirect water heater

Jo

I agree that this installation looks a bit odd.

Let's take a look at an example HTP (Heat Transfer Products)

HTP (Heat Transfer Products) Superstor Ultra INSTALLATION MANUAL [PDF] HTP, Inc Corporate Office, 272 Duchaine Boulevard, New Bedford, MA 02745 USA Tel: 800 323 9651 E-mail: sales@htproducts.com HTP Technical Support: 800-323-9651

Also see the HTP water heater manuals and information

at HTP HEATING & HOT WATER COMPANY -

Also see AMERICAN / AMERICAN STANDARD WATER HEATER AGE & MANUALS

I could not see all of the piping connections on your subject water heater, but we might compare it with both the manual and this excerpt example illustration (below)

Branching off of the Hartford loop (steam condensate return) is unfamiliar to me as well.
I've seen plenty of steam boilers that also fed hydronic heating baseboards on a lower floor level, but not indirect water heaters piped as the one in your example.

Your guess about piping a fill valve for the boiler at this remote location is not as wild as it might seem. Sometimes a tech looks across at an older boiler and figures that if she touches ANYTHING on the old boiler it's going to be a devil of a time: valves don't work, fall apart, etc.

So she might have figured OK I'll just install my own manual valve over here to fill the system right after my installation - it'll never be needed again (presuming the automagic water feeder on the steam boiler is kept working, flushed, etc.)

I am left SPECULATING that someone might have been regulating the flow rate of hot water through the heating coil in the SuperStor water heater - an arm-waving guess you could investigate by determining the position of that stop valve whose handle has been removed - is it fully open or only partly open - though just why is a question needing more research.

By the way, ball valves such as the one in your example are not designed to be operated at a partly-open position. They work best fully open or fully shut.

On 2018-02-26 by Anonymous

@Jopom, I'll add that technically this makes the WH loop a "slave," and the boiler's fill is a manual ball valve and located on the other side (no auto-fill)

On 2018-02-26 by Jopom

Inspected an HTP water heater indirectly heated by a steam boiler with something odd. There was a pipe installed which connected the heat coil loop to the cold water intake of the water heater, it had a valve in the middle of this pipe shut off with the handle intentionally removed.

Here's the setup: Brand new system installed last year. Fascinating how it was done. Steam boiler still heats the radiators in the original rooms, while 2 FHW zones heat the addition's living room and second floor beds.

These 2 zones are a separate loop with its own temp/press gauge, pressure reducing valve and backflow, and expansion tank.

This loop is heated by the tankless coil just below the water line (intended for hot water).

Now the loop for the water heater isn't closed, it branches off the boiler's side of the Hartford loop to it's own pump, then returns from the water heater to the front of the boiler near the bottom. No mixing valves in this setup, WH t-stat controls pump.

So back to my original question. Why would there be a pipe installed, stopped by a closed valve, that goes from the WH's cold water intake to the loop. Maybe it was an easy way to plumb a fill for the boiler but for some reason they chose against it? Thanks

On 2018-01-08 by (mod) -

Just be sure that we're not being fooled by having wired a heating zone up to a zone that thinks it's controlling an indirect water heater.

On 2018-01-03 by David

Thank you for your reply. I tried one more option. I shut off the heat in my basement which is a blower which also feeds off the boiler. As soon as I did that, I began to get hot water in the faucets and the shower.

Which tells me that your probably correct about the bad circulator.

If any other suggestion please let me know. Just a reminder. I have an Indirect system. Thanks again.

On 2018-01-03 by (mod) -

Sounds like a wiring error

On 2018-01-02 by Eric

My oil burner's indirect-fired hot water heater is Overheating.
The hot water tank thermostat (usually set about 10:00 position) will click on & off at the 3:00 position, after a scalding hot shower, will accurately click around 1:00 position - so I don't think it is a bad thermostat.

Could have screwed something up during oil boiler repairs last spring?

I am GUESSING that the hot-water pump is coming on every time a baseboard zone asks for heat, even though tank thermostat didn't ask for it. If so, DHW would have never overheated during hot summer; wouldn't have noticed during fall & early mild winter; but now that bone-chilling cold is (tripping a different zone thermostat every half-hour) it is hyper heating the DHW tank.

Not certain, but what could cause the DHW pump to come on every time the baseboard circulator pump comes on? What relay could be stuck or could a setting be screwed up?

On 2018-01-01 by (mod) -

The heating baseboards in your home are being heated by water circulating out of the heating boiler. The indirect fired water heater is heated buy a coil through which water from the heating boiler circulates. So if you have no domestic hot water at sinks or faucets but you do have heat in your house we suspect the control or circulator pump that keeps the water in your indirect water heater hot

On 2018-01-01 by David

I have an indirect system in my home. I'm getting hot water to the water base heaters and the basement. However, I'm not getting hot water in the water faucets and the shower. The house is heating up. Just not getting hot water in the faucets. What can this be?

On 2017-12-17 by (mod) -

Joe

You need to find the wiring or control error that's not turning on the circulator - as you say it's new I wouldn't expect the circ itself to be bad.

Watch out: your system might be in danger of overheating and thus be unsafe if you heat up the wood boiler without the circulator functional.

On 2017-12-12 by Joe

??My circulator between my wood fired boiler and my oil furnance will not operate how can I work around this problem. This is a new circulator

On 2017-11-13 by Kevin

My oil fired boiler, indirect hot water system stopped working. how to trip? or bridge the circuit to test the circulator pump function, before $$ replacing the pump.

On 2017-04-24 by (mod) -

Rocco:

Hot water is produced by cycling hot water from the hydronic or steam boiler through a loop of copper tubing that is located inside of a separate steel "domestic hot water" tank. The water in the hot water tank is thus heated by the physically separate hot water that is sent from the heating boiler, through piping, through the coil in the hot water tank, and back to the boiler.

In essence we're transferring heat from the boiler to the water in the separate hot water tank through that coil.

That's why we call it an "indirect" fired water heater. The "fire" is over at the home heating boiler, not directly in nor at the hot water tank itself.

This sketch from Carson Dunlop Associates (Toronto Home Inspection Educator & reprort writing tools) shows the arrangement

https://inspectapedia.com/plumbing/Indirect_Water_Heater023-CD.jpg

On 2017-04-24 by Rocco

How does an indiret fired water heater work ?

On 2017-01-04 by (mod) -

RE-posting

Question: why a water heater looses its oomph

2017/01/03 George alexander said:
I have a 23 year old weil mclain indirect storage tank that is losing its bang from previous years why does this happen over time


Reply:

George please search InspectApedia for WATER HEATER DE-SCALING to see likely causes and cures for the loss of heating capacity that you describe.

Question: How do I turn up the temp on my indirect fired water heater?

(Apr 18, 2015) Lesli said:
How do I turn up the temp on my indirect fired water heater?

Reply:

Lesli

Look for a thermostatic control mounted right on the heater tank itself - typically a gray metal box with a temperature dial.

Thanks to Carson Dunlop Associates, a Toronto Home Inspection Firm and Home Inspection Educator, for permission to use sketch shown here.

Question: Life span & replacement recommendations for an Amtrol Indirect Water Heater

(Apr 19, 2015) Elaine said:

I have an Amtrol Indirect Hot Water Heating System Model WH7L which was installed in 2000. I have never had a problem with it but I would like to know the expected life span.

It has a limited lifetime warranty "if I am the original homeowner-purchaser, for as long as you own and occupy the single-family home in which the Hot Water Maker has been installed", which I am.

The recommendations I read seem to indicate Hot Water Heaters should be replaced every 8 - 12 years. Does the same apply for Indirect Hot Water Makers?

Reply:

Elaine

Sorry to have to duck the question a bit but the life of water equipment varies quite a bit depending on such variables as the water chemistry (how corrosive is the water), the quantity used, flow rates, even temperatures.

The life of tanks varies further by the quality of protective coatings in the tank, the use or non-use of an internal bladder to keep water and air separate (not found on hot water tanks), and even installation snafus like mixing steel and copper piping at locations that invite corrosion and leaks.

Bottom line: it would be odd to replace a water heater tank before it needed replacement: the most common cause of replacement is the observation of a leak. So "should be replaced every 8-12 years" is a view principally benefiting people who sell and install the water heaters.

If a water heater were in a location where a leak would cost very costly damage - leaking over a collection of paintings by Diego Rivera for example - that would be an unacceptable risk. But rather than replace the tank prophylactically, most plumbers would instead install a catch-basin and drain system to assure that if the tank leaked it'd be discovered and the water handled without damage.

Question: white crystals forming on the hot water tank - pex piping warning

(Sept 15, 2015) Vinny D. said:
My Burnham Alliance Indirect Water Heater is roughly 11 years old. There's significant rust and corrosion on the TOP of the tank. Does this require a replacement tank? What would cause this on TOP of the tank?

(Oct 6, 2015) david bernier said:
i have a super stor that suddenly stopped producing hot water, luke warm at best. i turned up the aquastat, which helped. is it possible the aquastat is bad? the tank is only 3-4 years old. thanks

(Nov 10, 2015) Dave Maz said:
I have a white crystals forming on the hot fittings on the domestic side of an indirect hot water tank. The piping is pex with brass fittings. Any idea what is causing it?

Reply:

I sure do, Dave, it's likely to be a slow perforation of the brass fitting - you're seeing mineral salts left behind as water evaporates.

Details are at

inspectapedia.com/plumbing/PEX_Brass_Fitting_Leaks_De_Zincification.php

Please use our page bottom CONTACT link to find my email and send me some sharp photos of what's going on - I'll be able to comment further and what you show may help other readers.

Question: Weil McLain Gold Boiler with indirect water heater - not enough hot water and slow recovery time

(Nov 15, 2015) Dean R. said:
Hello,

I have a weil mcclain gold boiler with a PHCC 9048-609 indirect water heater. It's about 10 yrs old. The problem I'm seeing is after the hot water gets used up in the tank it seems t take a very long time (maybe an hour or so) for the hot water to regenerate.

It has 3 zones and one is the hw zone and all 3 zone valves were replaced recently so I know the valve is working fine.

What may be causing it to take so long for hot water to generate, could there be an issue with the PHCC controls?

Thanks, Dean

Reply:

Common issues are

the circulator is not turning on when it should

the controlling thermostat is not properly set or is defective

scale formation in or on the heating coil

the heating loop is air-bound

Question: not enough hot water from super store coil

Nov 28, 2015) Turkmfd@yahoo.com said:
Not getting any water out of supper store coil while trying to purge from boiled return. I'm thinking clogged coil? Any info?

Reply:

I would replace the coil and install a water softener

Question: where is the water heating cylinder anode?

Dec 31, 2015) dan said:
cant find anode on gold plus indirect hot water tank

Reply:

Dan

Gold Plus water heaters are a Weil McLain brand - the company will be glad to provide the installation and service manual for your model.

http://www.weil-mclain.com/

You may find that the dip tube is doing double-duty as the sacrificial anode. Some installations that use recirculating hot water use a dip tube in the AUX fitting at the water heater top. Otherwise the dip tube is usually at the cold water inlet.

Question: Slant fin weater heater needs aquastat

(May 15, 2016) stelianplesoiu said:

My 60 gal. Slant/Fin Water Heater need replacement of the Aquastat. The numbers are written on it are : Slant/Fin Water Heater (WH-60), 60 Gal. Model # 664115000 (WH-600, Serial # 15YG28F0071, Shop Order #2104 HoneyWell.

Can I can replace this one with Honeywell Aquastat L6006A ??? Thank you and appreciate your answer back.....stell p.

Reply:

Stelian perhaps the Honeywell L6006A1004/U aquastat.

See this PDF at our website inspectapedia.com/heat/Honeywell_L6006A_Aquastat.pdf for a description of the applications of this aquastat

Question: Honeywell Heat Flow indirect water heater leaks

(June 7, 2016) Casey said:
purchased a honeywell Heat Flow indirect fired water heater 2012 and now it is leaking, oil company that install said lifetime replacement, but not the Labor.

it will cost me over 600.00 to have install AGAIN., I paid over 1800.00 the first time. why would an expensive unit start leaking so quickly?

Reply:

Casey, I would examine the indirect water heater very very closely to pinpoint exactly where the leak occurred. That in turn may suggest the cause.

For example a leak at piping or connections could be due to poor installation or due to a water hammer problem; a leaky relief valve is a safety concern and may mean the system is being overpressurized.

Check for

corrosive water

improper electrical wiring or grounding

See WATER HEATER LEAK REPAIR

Question: cost of a 40 gal. indirect fired water heater

(June 7, 2016) KC said:
what is the cost of a 40 gal. indirect fired water heater, Honeywell brand

Reply:

Typical indirect water heater costs range from $600. to $1400 USD.

Question: can't turn off hot water

(June 10, 2016) Joanne said:
A few months ago I had an indirect water heating system installed to replace the gas hot water heater.

The gas heating system is about 7 years old. This is the first summer season with the new system. The heat remains on, even when the thermostat is set to low or turned off. I disconnected the thermostat and the heat is still on. Please advise.

Reply:

Joanne,

Ask your heating service tech to check for a flow-control valve that is stuck in or manually placed in the "open" position, for for a zone valve or other check valve that is stuck open.

With one or more such valves open on your heating system, when the boiler heats up to heat the water in the indirect water heater, hot water from the boiler may circulate by "gravity" (or as I prefer, by natural convection) even if the thermostats are not calling for heat and even though no circulator pump is running.

Question: run out of water in summer with indirect water heater

(Aug 22, 2016) T said:
I had an indirect- fired water heater installed two months ago. It is summer. Every four days, we run out of hot water. We have to turn the heat on for ten minutes to get water flowing from the home heat boiler system to the hot water tank. Is this supposed to happen? Was the system installed correctly?

Reply:

Sounds as if your boiler controls are not properly set or wired. For example if the boiler is shutting down when it should be keeping the boiler itself hot to make hot water then the control is not properly set.

Question: Alliance water heater gets too hot

(Oct 14, 2016) Lenny said:
My Alliance indirect hot water heater over heats. I replaced the thermostat on the heater with no change in the problem.

Reply:

Sounds like a wiring or control problem, and sounds unsafe to me. Check both thermostats.

Question: Weil McLain water heater, now no hot water

(Nov 3, 2016) Teng said:
I don't have hot water again .I have weil mclain hot water heater and boiler. The service guy just replaced cir.pump last week and it did work for a week. The problem comes back now. any suggestion? Thanks

Reply:

Call the service manager and ask for a more-experienced technician. I'm unsure what's wrong from just your etext

Question: which thermostats or controls are used on an indirect water heater

(Nov 20, 2016) marc said:
Q# thermostat or aquastat on indirect water tank? On an indirect water heater installation, which temperature control is to be used on the water tank, a thermostat or an aquastat when wiring to circulator?

Q# "Where" and "should there be" check or flow control valves installed (which loop)to prevent boiler water from circulating through radiators in summertime when thermostat is set way down?

Reply:

Marc I'm not sure I quite understand these questions but I'll take a stab at answers anyhow

Q#1 on an indirect water heater a limit control is typically mounted on the indirect water heater tank and in turn is used to turn on a circulator that circulates boiler water from the boiler through the indirect water heater tank's heating element when the water in the indirect water heater tank has cooled below the set point on the limit control.

Examples are at inspectapedia.com/heat/Boiler_Heater_Limit_Controls.php

Q#2: Using the search box just above and searching for "heating system check valves" you'll find

CHECK VALVES, HEATING SYSTEM inspectapedia.com/heat/Check_Valves_Heat.php that answer that question

Question: tankless coil vs indirect water heater

(Nov 20, 2016) marc said:

I'm trying to figure which is best, an indirect or a booster off the tankless coil in the boiler since running out of hot water in the shower seems to happen sometimes.

The biggest problem is cold or hot surges while taking a shower even after installing an anti scald shower body which is also supposed to compensate for pressure drops.

Also installed aerator restrictors at the sinks and ALSO reduced hot/cold flow to the fixtures at the shut off's. Thanks IA

Reply:

Please search InspectApedia.com for GET MORE HOT WATER where we discuss the properties of both of these heaters. Also search for ANTI SCALD VALVES as you surely need one .

Question: range boiler temperature control

(Dec 2, 2016) Steve said:

How is the domestic water temperature controlled in a range boiler? I working with such a system & there is a tempering valve installed at the tank to bring the temperature down to 120 before it's distributed.

The problem is, there is also a gravity circulation system that only works by using a bypass around the tempering valve. Sooo....there is always a slug of extremely hot water in the lines when a faucet is first used. I'm thinking the only solution is to somehow control the temperature in the tank. Thoughts?

Reply:

Traditional range boilers circulated and heated themselves by convection or "gravity" - the aquastat on the boiler is the temperature limit.

Question: why a water heater looses its oomph

2017/01/03 George alexander said:
I have a 23 year old weil mclain indirect storage tank that is losing its bang from previous years why does this happen over time

Reply:

George please search InspectApedia for WATER HEATER DE-SCALING to see likely causes and cures for the loss of heating capacity that you describe.

On 2014-09-08 by (mod) - indirect water heater acts as a separate heating zone as far as the boiler and its controls are concerned

Ah. But then an indirect water heater acts as a separate heating zone as far as the boiler and its controls are concerned. The boiler doesn't know it's heating a tank of water instead of a room.

On 2014-09-07 by Don F.

Dan, Not a heating zone. An HTP Superstor Contender indirect hot water heater zone.

On 2014-09-07 by (mod) - Modern circulators can tolerate being on the hot side but ...

Don

Modern circulators can tolerate being on the hot side but will most likely last longer on the cold or return side of the system.

The choice of using a reduced pipe diameter requires careful heat loss analysis and btu requirement analysis for the zone served.

That is a much bigger reduction in heat delivery than you may guess. I'm not sure what recovery time you mean; but generally if we can't get heat into an area fast enough, on the coldest days of the year the room may be too chilly as we've cut the BTUH delivery rate.

On 2014-09-07 by Don F

Not sure what you mean but, I think your saying is way back tech used the return side because of the lower temp extending ciruulator life. It's my understanding that this no longer the case because of better made circulators.

So please tell me your thoughts on reducing from 1" to 3/4". I think flow will be reduced to 4.9gpm and I am not sure how much slower recovery time will be.

On 2014-09-06 by (mod) - Bock Superstor™ indirect water heater piping

Don, locating a circulator on the return side is old price as thre it sees cooler temperatures, condition many techs opine increases circulator life.

On 2014-09-03 by Don F

The SSC35 is a HTP product called the superstor.

SSC35 drawings show the circulator mounted on the boiler supply hot side.

My current Bock indirect has the circulator mounted on the same side as the the expansion tank and air scoop, the return side. I'd like your opinion of the consequences of keeping the SSC35 circulator on the return side instead of the supply side?

The SSC35 calls for 1" pipe for the coil run. I can't easily convert from my present 3/4"coil piping setup. So I'd like to use the 1" coil piping up to the 3/4" Grunfos 15-42fr circulator and continue the 1" pipe after the circulator to the 3/4" in and out of the boiler. I'd like to know if this an acceptable approach?

On 2014-04-01 by (mod) -

John, the LO and DIFF become irrelevant because the indirect hot water tank is operating as another heating zone. In this case I might just disable the LOW (which also disables the DIFF).

For greatest efficiency I'd run the HI at close to 200F, reasoning that the thermal conductivity of hot water is exponentially greater at higher temperatures, both into the heating zones and into the little heating zone that's heating the hot water tank.

On 2014-04-01 by John

What should my boiler aquastat high, low, and differential settings be when using a indirect hot water tank.

On 2014-02-14 by (mod) -

David you made a good diagnostic step.

If disconnecting wires at the thermostat turns off the system then the issue is at the thermostat.mof you have to disconnect the thermostat wires at their other end, at the boiler or circulator then the wires may be shorted enroute.

Another direction of thought is the possibility that the temp sensor of the thermostat is debris covered.

Keep us posted.

On 2014-02-14 by David

My Alpine SL50 Indirect water heater thermostat is at temp (solid green light) but keeps the boiler running. Disconnected the 24v wires to the thermostat and the boiler shut down. Any thoughts?

On 2014-02-12 by (mod) -

Roland, a heat pump is an efficient source of energy, but just how efficiently it will work for you depends on your climate zone; in areas where outdoor temperature are quite low for long periods the efficiency of backup-heat or alternative heat becomes important as well. Search InspectApedia for "heat pumps" to read more about these systems.

On 2014-02-11 by roland

want to eliminate tankless coil in oil boiler with most efficient alternative to heat water. don't know too much about heat pumps

On 2014-01-29 by (mod) -

Carl, if your hot water is made by an indirect-fired water heater like the ones described in this article, I would check that valves between the boiler and the hot water tank are open, and that the circulator for the hot water tank and its relay control will operate. Keep us posted.

And if you want to send me photos that show details of the installation I can comment further - use the CONTACT link found at page bottom or page top.

On 2014-01-29 by Carl

I had a busted pipe in the basement and emptied out the boiler. After it was fixed I get heat but no hot water

On 2013-01-22 by Al

I am thinking of an indirect tank with 2 coil heat exchangers. One connected to an alternative heat source such as solar or compost and the other to the boiler as a backup and to maintain the water at a safe temperature level.

I currently have a 8x12x5 compost bin filled with horse manure that has a temperature between 140 and 160 degrees in the center 24/7. Does a setup like this sound feasible?

On 2012-11-25 by Andrew

I have a fairly new 40 gal wieler mclain indirect storage tank that worked fine until I renovated. I added a second shower head to my shower and now I go through the hot water quickly. My question is can I add another indirect storage tank in tandem with the one that I already have or do I have to replace the one I have with a bigger one?

On 2012-11-09 by Phil

Is my tank in need of replacement if its leaking water from the control well pipe? Or is that fixable? Nothing else is wrong. It's a Superstor 40
Thanks

On 2012-11-09 by (mod) -

Diane, it depends. What wiring ? Thermostat or 120v?

For example an installer often will tape thermosat wires onto any convenient but secure building or plumbing component in the area where those wires are routed. That's generally acceptable (as long as the wires are not being heat-damaged) for low voltage (24VAC) thermostat wires.

On 2012-11-09 by DIANE

Is it common to attach wiring to hot water copper pipes on the indirect fired boilers without protection of wiring?

On 2012-10-22 by frankky

my indirect water heater don't turn on it seem to turn on and off but it does not stay on what seem to be the problem?

On 2012-10-08 by (mod) -

Raul
Gheck for a defective water feed/pressure reducing valve, a valve left in bypass mode,nor a leaking tankless coil leaking into the boiler.

On 2012-10-07 by raul

can't get my psi to stay under 30psi. have to keep my return heating return valve close or the t/p relief valve opens.

On 2012-09-18 by David

So which company offers the best price to quality ratio for indirect water heaters?

On 2012-08-04 by (mod) - typical indirect water heater piping basics

Jim you'd need to send me a sketch of your idea;

In the indirect water heater hookups I've seen we have 4 pipes:

- cold water into the water heater tank from the water supply source

- hot water out of the water heater tank into the home

- a pipe bringing hot water from the heating boiler into a heat exchanger located inside the hot water heating tank

- a return pipe returning water from the in-water-heater-tank heat exchanger back to the heating boiler to be re-heated

On 2012-07-31 by jim

is there a way to do a three pipe indirect water heater

On 2011-10-03 by (mod) -

Romeo,

Usually there are control valves that will stop sending water through the tankless coil, or you can search InspectAPedia for AQUASTAT WIRING and review our procedure for disabling the LO circuit that keeps the boiler hot for domestic hot water and a tankless coil.

For the indirect water heater, turn off power to its circulator.

Be sure you've freezeproofed the building.

On 2011-09-09 by Romeo Nadeau

I have a New York Boiler with a tankless coil for DHW, I also have an indirect electric hot water heater in the circuit.

I'm leaving this winter for 4 months and I'm wondering if there is someway to shut down the DHW circulation in the boiler,as I only want to heat the house at a minimum and no DHW will be used. I plan on disconnecting the elictric hot water heater. Thanks for any help

On 2011-08-11 by (mod) - thinking of switching to electric hot water and doing away with tankless coil.

Paul electric water heaters are generally least costly to install and most costly to operate compared with oil and gas fired water heaters in most communities (your electric rates may be different). But going to a tank-type water heater can give more total hot water than most tankless coil water heater systems.

Though it's more costly to install than electric, you might consider an indirect-fired water heater instead. That adds a tank of hot water that is heated indirectly by your existing boiler, a more efficient design that gives plenty of hot water.

The article INDIRECT FIRED WATER HEATERS describes indirect-fired water heaters.

TO disable the tankless coil circuit on the boiler you will want to read about disabling the DIFF function on the aquastat that controls your boiler.

We explain more about the DIFF function in detail at Aquastat control DIFF settings. And for boilers that do not use a tankless coil to make domestic hot water, at Disabling the LO and DIFF settings we explain how and why you might want to disable these controls.

Those articles are linked at page bottom ARTICLE INDEX . See

AQUASTAT CONTROL Functions
and beneath that heading see Aquastat control DIFF settings where we discuss disabling that control

On 2011-08-10 by Paul

I am thinking of switching to electric hot water and doing away with tankless coil. Is this wise and how do I disable the boiler?

...

Continue reading  at INDIRECT FIRED WATER HEATERS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• HOT WATER QUANTITY IMPROVEMENT
• INDIRECT FIRED WATER HEATERS
  • DEFINITION of INDIRECT WATER HEATER
  • INDIRECT WATER HEATER COIL LEAKS INTO the BOILER
  • INDIRECT WATER HEATER PLUMBING CONNECTIONS
  • INDIRECT WATER HEATER TEMPERATURE CONTROLS
  • INDIRECT WATER HEATER EFFICIENCY
  • INDIRECT WATER HEATER LEAKS
  • INDIRECT WATER HEATER REPAIR
  • INDIRECT HOT WATER HEATER TEMPERATURE CONTROL
• TANKLESS WATER HEATER INSTALLATION
• WATER HEATER AGE & MANUALS - free PDF downloads of water heater installation & repair manuals
• WATER HEATER LEAK REPAIR

Suggested citation for this web page

INDIRECT FIRED WATER HEATER FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to WATER HEATERS

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