Questions & answers about diagnosicing & fixing tankless hot water coil leaks & corrosion.

In this article series we explain how to spot, evaluate, and repair leaks at the tankless coil used on heating boilers to provide domestic hot water or leaks in the hot water heating coil used on indirect-fired water heaters.

Tankless Coils & Indirect Water Heater Coil Leak FAQs

These questions & answers about the cause, spotting-of, & repair of leaky hot water tankless coils were posted originally atTANKLESS COIL / HOT WATER COIL LEAKS - take a look there: you'll be glad.

On 2016-12-01 by (mod) - repairing a pinhole leak in copper

Isaac you can sometimes repair a small pinhole leak in copper piping by soldering.

I'd want to understand the cause of the leak to be sure the repair is appropriate.

On 2016-12-01 by Isaac

Can a leaking coil (no corrosion) be repaired by applying the same non-lead flux applied to connect lengths of tubing?

Thanks

On 2016-04-20 by (mod) - Rheem backs their leaky water heater

Diane:

I'm impressed at Rheem's backing of their product. If it's true that the leak problems are unusual - and it sounds that way - I'd sure want to know why before installing ANY new water heater. I'd sure want to do what you suggest: dissect the water heater to look closely at what exactly failed and to try to figure out why.

Examples - I AM MAKING THESE UP as SPECULATION

- uneven mounting on a wall or uneven torquing of mounting bolts stressing the heater components

- hard water forming scale deposits causing uneven heating of the heater's heat exchanger

- aggressive water chemistry (corrosive)

- excessive use?

As it's easy to do so, I'd have your water tested for hardness, corrosivity, and ask the lab if water in your area has been found to have anything else that's unusual that they would add to the testing.

If you can find a decent forensic expert who can cut an old heater apart - or maybe Rheem would agree to do it - if scale or uneven mounting are at fault those causes should be self-evident on examination.

Rheem may be afraid of bad PR - you'd have to convince your rep of goodwill and trust. Or they may have already looked: did your old heaters go back to Rheem?

On 2016-04-19 4 by Diane Sparks

I have a Rheem tankless hot water heater. Rheem has replaced my heater 3 times, I am on my 4th heater in seven years! It is now malfunctioning, same problem,

Leaks! It is now out of warrenty. Rheem tells me they've never had problems like mine, none of the 3 plumbers, rheem certified, I've had out here to look over the years has ever heard of one leaking.

Mine begins to leak from the back of the unit, no one has dissected an old one to find out why, of course. Once it begins to leak, within a week it will short out the fuse near the fan and not come back on. this time I will have to purchase a new unit myself. Looking for suggestions

. It was suggested that my water is too hard, the last plumber tested it to be a 7, hard, but not out of range. Suggested too much use, but we operate within range, top of range but within range. Now plumber thinks another chemical, in our water is causing breakdown, of what no one knows. we are at a loss. supposedly installation is correct. We flush unit with water every 6 months or year.??

On 2016-01-06 by (mod) -

Robin:

Some tankless coils are indeed mounted through a rectangular plate, though the coil inside is still usually a round system; a few use a horizontal "back and forth" tube design; all work in a similar fashion.

I'm not sure why anyone would remove a coil for flushing it; in my experience the plumber connects fittings to the coil in- and out- lines by adding stop and drain valves if they're not already present, then she uses a pony pump, de-scaling liquid, and a plastic bucket to cycle the de-scaler thorugh the coil, ending by flushing it with clean water.

The bolts on a coil would not be expected to pass all the way through the boiler face into the boiler itself but perhaps on your boiler they do. So indeed one might try this:

turn off heat

let the boiler cool

drain pressure off of the boiler but don't empty it

start removing one coil bolt: as it loosens if you see water coming out of the hole, stop, turn it back in, and drain enough water from the boiler so that the water flow at the bolt(s) stops.

Remove the bolt: inspect for stripped, damaged threads; if the bolts are stripped more troublesome boiler repairs are needed (or your plumber will argue for replacement);

if the bolts are in good shape the hole into which they screw may be OK too.

You can try teflon tape or a pipe sealant that tolerates heat and high pressure on the bolt threads; turn the bolt back into place. Re-fill the boiler, turn it on and look for leaks;

I know it's a lot more trouble but I'd be tempted to try one bolt before fooling with all of them.

Actually I still suspect a bad gasket or bad coil mounting surface at the boiler. If the section of gasket between the bolt hole and the inner circumference of the gasket is not in good shape that's where boiler water might leak into the bolt hole.

If I'd hired a plumber to de-scale a tankless coil that was not leaking at all before the repair, and if it leaked afterwards, I'd expect the plumber to return and finish the job by repairing the leaks. I'd understand if he or she argued that the boiler and coil were old and in poor shape and that they were unavoidably damaged during removal of the coil - that could happen, though I still don't get why the coil was removed.

On 2016-01-06 by Robin Thompson

My furnace guy cleaned the surface and the plate to get a good seal. I don't have a round coil it's rectangle. Just think it's strange to be leaking around the bolts. I know over tightening is not good either. It didn't leak until the coil was pulled out to be flushed because I had no hot water pressure. Have hot water pressure now.

Thank you for your prompt replies. Wonder if putting plumbers tape on the bolts would stop them from leaking? I guess eventually some day I'm going to have to replace my boiler, but need one to heat the hot water and garage too.

On 2016-01-06 by (mod) - understand the nature of long-standing leaks at the tankless coil mounting plate

Robin

Usually the round coil plate is quite thick and not likely to be warped such that it can't be bolted properly.

More likely is that leaks around the coil face plate corroded the plate itself or corroded the mating surface on the boiler itself. If the boiler face is badly corroded it may be very difficult to get a good seal even when a new coil is installed. The way to find the problem is to turn off and drain the boiler, remove the coil face plate, and examine the mating surfaces.

On 2016-01-05 by Robin Thompson

I have a Burnham boiler and it's 25 yrs old. Would replacing the heat coil stop the leaking around the bolts?

Maybe the heat coil plate is damaged somehow or warped? Expensive fix though, but cheaper than buying a new boiler. It's not a big leak and I keep a pan under the boiler to try to catch what leaks, but some still ends up on the floor from run off. Just don't want it to cause more damage to the boiler if that would happen.

On 2016-01-05 by (mod) -

Robin:

I don't know why - with so little actual information about conditions at the boiler, but some examples of persistent leaking at a coil, presuming the leaks are occurring around the outer perimeter of the coil mounting plate and not at the pipe connections, include improper gasket, omission of gasket sealer, or a badly-corroded mounting face on the boiler itself. If the prior coil leaked for a long time the boiler could itself have been damaged.

On 2016-01-05 by Robin Thompson

The heat coil was removed and cleaned out due to it being clogged. New gasket installed. Leaked around gasket.

Guy came back, tightened bolts and still leaked. Put new gasket and sealer on. Worked for about a month then started leaking again around the bolts. I tightened them just enough to stop the leaking. This worked for a while and now it's leaking again around the bolts. Why?

On 2015-04-28 by (mod) - low chance of successful repair of corroded tankless coil

Doug:

becausae of the nature of corrosion in coils the chances that a leaky one is repairable in this circumstance are close to nil. Add the fact that the labor cost to remove and replace the coil is significant and the reasonable conclusion is: replace the tankless coil.

On 2015-04-28 by doug

My boilermate!!!! I think it is the coil leaking and backfeeding my boiler causing high pressure in the boiler. I can hear cold feed pipe running into the boiler mate. When I shut the ball valves it seems to stop.
Is it worth trying to fix it,,(new coil) or get a new one?

On 2015-04-28 by Anonymous

I have a pressure problem and I can hear the water feed to the boiler mate running. The boiler blew out the Pressure valve. Is it possible to replace the coil inside? or get a new one?

On 2014-12-26 13:30:55.700080 by Marlon

Thanks for the diagnosis procedure, which helped me to find the dripping issue related to leaky tankless coil. Now, my question is: I want to completely abandon the tankless coil water heater, and install a stand-alone water heater (new heat pump type), Is it possible to plug the water inlet and outlet on the mounting plate (without removing the tankless coil inside the burner water?

On 2014-12-11 14:43:42.318680 by Colin

My oil fired hot water boiler is equipped with 2 Taco 007 circulators supplying hot water to 2 zones of the house as well as providing domestic hot water for the shower and sinks.. Recently I've noticed that even with the zone 1 room thermostat set way low, the boiler continues to kick on and keeps the baseboard heaters warm. Does this sound like a problem with the circulator pump? The service valve located on the boiler side of the pump seems to have some rust build up at its connection with the water pipe leading from the boiler itself. Might that be the issue? Any help someone could provide is greatly appreciated.

On 2014-11-24 22:52:15.532810 by (mod) -

Anon, with just the info in your question I cannot agree with removing a temperature /pressure relief valve. Those devices are there to prevent a potentially catastrophic system BLEVE explosion.

If a needed relief valve is leaking the valve should be replaced, and if the new valve leaks the cause needs to be found and fixed.

Since you are asking this question in an article about tankless coil sim guessing your two safety valves are on different equipment or piping or tank systems.

See relief valve leak guidance in detail at https://inspectapedia.com/plumbing/TP_Valve_Leaks.php

On 2014-11-24 01:57:57.089230 by Anonymous

Hello we had our boiler cleaned about 3 months ago. Soon after cleaning, we noticed water dripping from a relief pipe. We have two? One for the heat and one for hot water?

Plummer said it was not required. He also noticed that temp was set too high and he lowered it to normal. The pipe is still leaking, and is worse when heat is not on. Should we just remove this pipe and plug it as the plummer is suggesting? Boiler is working great mormally

On 2014-05-24 02:48:29.172420 by (mod) -

Frank if the old coil leaked into the boiler that would spill the relief valve and put water on the floor.
If there are other boiler leaks I. The boiler itself, ask the plumber to show them to us.

Is this a cast iron boiler or steel?

On 2014-05-23 16:16:18.645640 by Frank 05/23/14

I would like to chage a new tankless coil, but one plumber recommended me to buy a new boiler. He told me that the boiler itself is weak and might have small cracks,as evidenced by the observation of about two cups of water from underneath the boiler and wetted insulator there, during cooling of the syetem after power had been shut down.

So I do not know whether the plumber is right or there are other explanations. In other words, whether it is worth to change a new tankless coil. Could you help explain? Thank you very much!

On 2014-05-23 16:00:37.157270 by (mod) -

30 psi is not normal it's high which says the valve was working as it should.

Look for a leak from tankless coil into the boiler.

On 2014-05-23 14:53:59.744060 by Frank 05/23/14

I have a 31-yeay oil boiler (tankless water heater), which had water dripping from the pressure relief one week ago. The pressure and temperature reading was as usual as 30 psi and 180 degree. After I shut down the power, there was no water dripping from the pressure relief anymore. But with temperature decrease to room temperature a few hours later, I noticed about two cups of water spread the floor from underneath the boiler bottom where the insulator became wet.

Changing the pressure relief valve and feed water regulator did not eliminate water dripping from the pressure relief. It seems that the issue is related to the coil inside the boiler.

My question is why cooling the boiler system has caused leaking of about two cups of water from underneath the boiler bottom where the insulator became wet. One explanation is attributed to compaction with cooling of the gasket to the problematic coil. The other explanation is that the boiler itself is weak and might have small cracks. Is there any way to differentiate these two root causes and are there other explanations? Thank you very much!

On 2014-03-01 03:45:37.061710 by (mod) -

Anon I don't quite understand the problem but if you are asking if water in the boiler is entering the tankless coil, that would be unusual; normally the building water pressure (in the hot and cold water piping) is at 20-70 psi; a home heating boiler is at around 12 psi cold and would not exceed 30 psi without spilling at the temperature relief valve.

On 2014-02-28 16:58:15.271580 by Anonymous

I have brown water coming out of the hot water faucet is it possible that my home heating water is getting into my tankless hot water heater coil

On 2014-01-31 12:55:53.154470 by (mod) -

Bill that sounds sensible. I'd like to see sharp photos of the coil faceplate too.

On 2014-01-31 10:06:46.904410 by Bill

Thanks for the information. From just looking at the faceplate the rust doesn't seem too bad but I know I won't know the extent of the rust until I remove the plate. I will wait for the heating season to be over before I try this. Thanks again for getting back to me

On 2014-01-29 21:27:04.694260 by (mod) -

Bill,

I would not try this repair if it is bitterly cold outside as you could end up with the boiler shut down for a time or even destroyed - it depends on how severe the tankless coil leak is, how corrosive is the water, and how long it has been leaking.

IF visual inspection makes you think that the boiler is not severely corroded then it may be possible to disconnect the pipes, remove the coil, pick up a replacement tankless coil gasket from your plumbing and heating supplier, seal the new gasket and bolt the coil face plate back in place.

Check the repair for leaks and check again at full boiler pressure and check again in a day - then watch it every few days too since a subtle leak may take time to make itself visible.

A separate topic is abandoning the tankless coil, installing an indirect fired water heater as another zone connected to the boiler - a solution that gives more hot water and may be more efficient.

In the More Reading links above we have placed links to articles that describe each of those options.

On 2014-01-29 13:43:36.037340 by Bill

I have a Burnham oil fired boiler V-14 A-T. It's about 30 years old. I'm leaking water from the top of the tankless coil face plate. If I am able to remove the plate can I get a gasket for this if so do I use any other sealant with the gasket. Also, I might want to install a separate electric hot water heater. I read some of the information you have on this. Is there an aquastat I can replace mine with that will just serve for heat and not hot water.

Question: Home Depot "experts" said that repairing a tankless coil leak is impossible - but I used radiator heavy duty stop-leak from an auto parts store

went to home Depot asking if there is any way to fix my boiler coil’s water leak. They looked at me like an idiot. No way can you fix the coil, they said. You must change it.

Then I thought of how to fix it the cheapest way. It did cost me $5.00 to fix it.
Here is what you do:

1- Shut off the boiler electrical switch and Close all valves around the boiler.

2- Drain the boiler from any water left.

3- Fill the coil (From any possible water inlet to the boiler) with Radiator Heavy Duty Stop Leak (Find it in any auto supply store).

4- Add about one liter warm water to the same inlet.

5- Switch on the boiler and let it run till the thermostat shut the fire off. The higher temp setting the better result you’ll get.

6-Shut off the boilers electrical switch and Let it cool down for 20 minutes.

7- Repeat the same twice more.

8- Now open the valves and let the boiler filled with water.

9-Some water may come out through expanding the cold water when it is heated for the first time only but the coil will be sealed for many years to come.

Repeat it after few years when it happened again.

You can use the same to stop auto radiator small leaks.

Sorry plummers. Enjoy it home owners.... :)

Talal Mikhail 4/1/12

Reply: Bad repair - you risk poisoning building occupants; don't try oatmeal in the tankless coil either.

Thanks for this interesting, if questionable repair idea for leaky tankless coils. It needs some clarification.

Leaks into the boiler: a tankless coil may develop a leak in the finned copper tubing that is inserted into the heating boiler interior. Such a leak will send household water supply into the boiler, causing excessive pressures in the boiler, perhaps showing up as a leaky boiler pressure / temperature relief valve, or as abnormally high pressure on the boiler pressure gauge. This is the sort of leak the reader below is describing.

We are not sure what the effect may be on the heating boiler, circulator pumps, zone valves, relief valve, of the passage of any stop leak compound into those components through the leaky coil before the leak stops - those may be harmful. Auto radiator stop leak is not designed for this circumstance

. It might work but it leaves me a little worried.

The second type of tankless coil leak, and the one illustrated on the page above, is a leak of heating boiler water out of the boiler around the tankless coil mounting plate or bolts.

This leak, as you can see in our photos, destroys the boiler if it is not found soon enough, and destroys the tankless coil mounting plate - an integral part of the assembly.

That's why the Home Depot rep was dead right when he said "replace the coil" - she or he was thinking of this common leak. Auto radiator "stop-leak" products won't fix this problem, and in fact running a stopleak product through the coil is irrelevant because that's not where the leak is found.

Old timers used to run oatmeal through the car radiator, and there is a similar lore of magic leak fixes that were applied to cast iron boiler leaks.

But for a corroded, leaky tankless coil around its mounts, you have to catch the leak early, remove the coil, clean up the mating surfaces, install a new gasket and reassemble. If you wait long enough, it's new boiler time.

On 2014-12-26 by Marlon

Thanks for the diagnosis procedure, which helped me to find the dripping issue related to leaky tankless coil.

Now, my question is: I want to completely abandon the tankless coil water heater, and install a stand-alone water heater (new heat pump type), Is it possible to plug the water inlet and outlet on the mounting plate (without removing the tankless coil inside the burner water?

On 2014-12-11 by Colin

My oil fired hot water boiler is equipped with 2 Taco 007 circulators supplying hot water to 2 zones of the house as well as providing domestic hot water for the shower and sinks.

Recently I've noticed that even with the zone 1 room thermostat set way low, the boiler continues to kick on and keeps the baseboard heaters warm. Does this sound like a problem with the circulator pump?

The service valve located on the boiler side of the pump seems to have some rust build up at its connection with the water pipe leading from the boiler itself. Might that be the issue? Any help someone could provide is greatly appreciated.

On 2014-11-24 by (mod) -

Anon, with just the info in your question I cannot agree with removing a temperature /pressure relief valve. Those devices are there to prevent a potentially catastrophic system BLEVE explosion.

If a needed relief valve is leaking the valve should be replaced, and if the new valve leaks the cause needs to be found and fixed.

Since you are asking this question in an article about tankless coil sim guessing your two safety valves are on different equipment or piping or tank systems.

See relief valve leak guidance in detail at https://inspectapedia.com/plumbing/TP_Valve_Leaks.php

On 2014-11-24 by Anonymous

Hello we had our boiler cleaned about 3 months ago. Soon after cleaning, we noticed water dripping from a relief pipe. We have two? One for the heat and one for hot water? Plummer said it was not required. He also noticed that temp was set too high and he lowered it to normal. The pipe is still leaking, and is worse when heat is not on. Should we just remove this pipe and plug it as the plummer is suggesting? Boiler is working great mormally

On 2014-05-24 by (mod) -

Frank if the old coil leaked into the boiler that would spill the relief valve and put water on the floor.
If there are other boiler leaks I. The boiler itself, ask the plumber to show them to us.

Is this a cast iron boiler or steel?

On 2014-05-23 by Frank 05/23/14

I would like to chage a new tankless coil, but one plumber recommended me to buy a new boiler. He told me that the boiler itself is weak and might have small cracks,as evidenced by the observation of about two cups of water from underneath the boiler and wetted insulator there, during cooling of the syetem after power had been shut down.

So I do not know whether the plumber is right or there are other explanations. In other words, whether it is worth to change a new tankless coil. Could you help explain? Thank you very much!

On 2014-05-23 16:00:37.157270 by (mod) -

30 psi is not normal it's high which says the valve was working as it should.

Look for a leak from tankless coil into the boiler.

On 2014-05-23 by Frank 05/23/14

I have a 31-yeay oil boiler (tankless water heater), which had water dripping from the pressure relief one week ago. The pressure and temperature reading was as usual as 30 psi and 180 degree. After I shut down the power, there was no water dripping from the pressure relief anymore. But with temperature decrease to room temperature a few hours later, I noticed about two cups of water spread the floor from underneath the boiler bottom where the insulator became wet.

Changing the pressure relief valve and feed water regulator did not eliminate water dripping from the pressure relief. It seems that the issue is related to the coil inside the boiler.

My question is why cooling the boiler system has caused leaking of about two cups of water from underneath the boiler bottom where the insulator became wet. One explanation is attributed to compaction with cooling of the gasket to the problematic coil. The other explanation is that the boiler itself is weak and might have small cracks. Is there any way to differentiate these two root causes and are there other explanations? Thank you very much!

On 2014-03-01 by (mod) -

Anon I don't quite understand the problem but if you are asking if water in the boiler is entering the tankless coil, that would be unusual; normally the building water pressure (in the hot and cold water piping) is at 20-70 psi; a home heating boiler is at around 12 psi cold and would not exceed 30 psi without spilling at the temperature relief valve.

On 2014-02-28 by Anonymous

I have brown water coming out of the hot water faucet is it possible that my home heating water is getting into my tankless hot water heater coil

On 2014-01-31 by (mod) -

Bill that sounds sensible. I'd like to see sharp photos of the coil faceplate too.

On 2014-01-31 by Bill

Thanks for the information. From just looking at the faceplate the rust doesn't seem too bad but I know I won't know the extent of the rust until I remove the plate. I will wait for the heating season to be over before I try this. Thanks again for getting back to me

On 2014-01-29 by (mod) - leaking water from the top of the tankless coil face plate.

Bill,

I would not try this repair if it is bitterly cold outside as you could end up with the boiler shut down for a time or even destroyed - it depends on how severe the tankless coil leak is, how corrosive is the water, and how long it has been leaking.

IF visual inspection makes you think that the boiler is not severely corroded then it may be possible to disconnect the pipes, remove the coil, pick up a replacement tankless coil gasket from your plumbing and heating supplier, seal the new gasket and bolt the coil face plate back in place.

Check the repair for leaks and check again at full boiler pressure and check again in a day - then watch it every few days too since a subtle leak may take time to make itself visible.

A separate topic is abandoning the tankless coil, installing an indirect fired water heater as another zone connected to the boiler - a solution that gives more hot water and may be more efficient.

In the More Reading links above we have placed links to articles that describe each of those options.

On 2014-01-29 by Bill

I have a Burnham oil fired boiler V-14 A-T. It's about 30 years old. I'm leaking water from the top of the tankless coil face plate.

If I am able to remove the plate can I get a gasket for this if so do I use any other sealant with the gasket. Also, I might want to install a separate electric hot water heater. I read some of the information you have on this. Is there an aquastat I can replace mine with that will just serve for heat and not hot water.

...

Continue reading  at TANKLESS COIL / HOT WATER COIL LEAKS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Tankless hot water coil Articles

• BOILER LEAKS CORROSION STAINS for a discussion of other leaks on heating boilers.
• RELIEF VALVE LEAKS
• TANKLESS COILS
  • AQUASTAT CONTROL FUNCTIONS
  • CLOGGED PIPES / TANKLESS COIL DE-SCALE
  • MIXING / ANTI-SCALD VALVES
  • TANKLESS COIL ANTI-SCALD-VALVE
  • TANKLESS COIL CLOG DE-SCALE
  • TANKLESS COIL CONVERSIONS
  • TANKLESS COIL HOT WATER HEATER TEMPERATURE CONTROL
  • TANKLESS COIL HOT WATER INCREASE
  • TANKLESS COIL INSTALLATION PROCEDURE
  • TANKLESS COIL INTERNAL LEAKS INTO the BOILER
  • TANKLESS COIL / HOT WATER COIL LEAKS
• WATER HEATER LEAK REPAIR

Suggested citation for this web page

TANKLESS COIL / HOT WATER COIL LEAK 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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