Heating Boiler Expansion Tank Leak FAQs

Diagnostic questions & answers on leaky or water-logged boiler expansion tank service & repair

Expansion Tank Leak FAQs

Tip: See EXPANSION TANK LEAK REPAIRS

Why would my heating system's expansion tank lose its air after just 3 or 4 days - the sight glass fitting shows no air

What makes expansion tank lose air in 3-4 days.

I checked for air leaks with soap bubbles around tank and sight glass fittings, found none.

Serviceman says domestic hot water coil may be leaking. How does that make tank lose air? Replacing coil will be expensive because of position of furnace. - J Warden 10/1/2012

Reply:

J Warden, I have to agree that I'm confused by this question.

The only hot water heating system whose expansion tank included a sight glass (a feature I find on steam boilers) was at a remote attic expansion tank serving a very old hot water heating system.

Above we illustrate this type of antique expansion tank, also sporting a sight gauge. This tank is installed in a Nazareth Pennsylvania home built in 1890, photo courtesy of home inspector Lawrence Transue.

Take a look at ATTIC & ANTIQUE EXPANSION or HEADER TANKS  and tell me if that's what you have.

Can you give me some details: boiler brand, type, model, and some photos to allow further comment?

In any case, if your expansion tank (if that's what we've got here) is losing its proper air charge every few days, there is either a leak out of the tank piping and fittings.

What do I need to do after my contractor removed an attic expansion tank?

Would you be able to help me determine what to do when my contractor removed my tank. I'd like to send you a before and after photos if possible? - Contractor removed attic tank 7/8/12

Reply: check that the removal was done properly - as we list here

We will try.

You may not need to do anything, if the contractor also

• Closed off / capped any open heating water pipes that entered the attic
• Made sure that the boiler is served by a modern expansion tank, probably located right at the boiler
• Made sure that the boiler's operating pressure and temperature range are correct
• Checked the boiler's pressure/temperature relief valve installation location and operation

Watch out: the steps above are important for safety.

Use the CONTACT US link at page top or bottom to send photos for comment, best accompanied by a specific question or concern.

Keep in mind that if your building is quite old there may have been an old, unused, atmospheric pressure expansion tank in the attic.

Expansion Tanks Needed ?

Do I really need an expansion tank on my boiler?

Can a boiler operate without a expansion tank? (Nov 10, 2014) Anonymous

Reply:

Watch out: The boiler will "run" but not operate properly without SOME means to handle thermal and air expansion in the water in the system - else it will dump the relief valve, that itself leading to an unsafe system.

Older boilers sometimes used a pressure overflow system that would simply dump boiler water at a safe location from an upper building floor.

The pressure in the system was set by the piping height. No modern heating boiler uses such a system nor would it be considered safe by modern standards.

Do I need a separate expansion tank for my electric water heater?

I have a Hot Water Boiler heating system with an expansion tank. I am now installing an electric water heater.

Does this need a separate expansion tank? Thank you. (May 31, 2014) Matt

Reply: possibly, yes

You might, Matt, depending on local regulations and the operating properties of your system, including water pressure.

Take a look at our article on the topic:

HOT WATER EXPANSION TANKS

and let me know if questions remain.

You'll see that for use on domestic hot water systems, the expansion tank such as the Falcon brand shown here are specifically designed for use on potable water supply systems.

Expansion Tank Location FAQs

Tip: For help finding the expansion tank on your system see FIND the EXPANSION TANK.

Tip: If yours is an old heating system the expansion tank may be remote: see ATTIC & ANTIQUE EXPANSION or HEADER TANKS and if that tank is removed be sure the boiler has a relief valve and a local expansion tank.

Check the installation instructions for your expansion tank to confirm its location and mounting position. If you don't have the manual for your expansion tank you can download a free PDF copy at BOILER EXPANSION TANK INSTALLATION & OPERATION MANUALS

Our sketch shows a typical location for an Amtrol Extrol thermal expansion tankon a heating boiler system.

Expansion tank installation location & pre-charge pressure?

Hi there and thanks for running this site. Great resource since hydronic heating is not commonplace in the US yet (at least not in CA).

I am trouble shooting a broken brass fitting on my hydronic system and here is what I found:

- The valve to the Extrol expansion tank was shut-off

- The expansion tank (and the air trap) are on the return side and not the supply side

Here are my questions:

- Is the return side installation of the Extrol tank a serious issue?

- What is the right pressure to preload the entire system (My heating system is in a basement in a two story above ground house)?

- Is there ever a need to check pre-load charge of the Extrol tank in accordance of the set system pressure (see above)?

BTW, the brass fitting burst during the summer month without any system load (it is a weak fitting - or rather connector type element - most likely not suited to the application).

Thanks for your answers in advance, Swen (Oct 18, 2014)

Reply:

Swen:

The Extrol tank comes pre-charged at the factory recommended pressure and will work on either side of the boiler water circulating loop but I would indeed prefer to follow the manufacturer's instructions - as described in the article above.

Probably 12 psi cold is the start pressure you need, but first read the details of how to decide on and set heating boiler pressure found in our article at

PRESSURE & TEMPERATURE SETTINGS, CONTROLS 

Expansion Tank / Compression Tank Location Recommendations

I want to install an Amtrol EX-30 expansion tank on cooler return side of the boiler

I need to install an Amtrol EX-30 expansion tank on a boiler that has the circulating pump on the return side of the boiler. I am confused as to where it should be installed?

I would think it should go on the supply side with the hotter water and thus more thermal expansion. Any advice would be appreciated.
Thanks! (May 8, 2016) Bruce Benner said:

Reply:

Bruce,

In a water piping system filled with water, excluding surges when valves open or close, water pressure is pretty much the same throughout the system.

But a look at Amtrol's Extrol hydronic expansion tank shows this instruction from the manufacturer:

"Install the EXTROL on the supply side of the boiler, on the suction-side of the heating circulator(s) (Figure 2)."

That means the Amtrol Extrol tank is typically installed on the hot side of the boiler, close to the boiler, on the hot water supply pipe ahead of the circulator pump(s).

In the live in this article series (or by searching InspectApedia.com for this captialized phrase) see the article

titled AMTROL's EXTROL®, the FILL-TROL® where you can find the manufacturer's installation instructions as PDF files in the article's REFERENCES section. There and in our article itself you'll see that typically the expansion tank is on the supply side.

Here is a direct link to Amtrol's installation instructions:

• Amtrol, "Extrol® Hydronic Expansion Tanks for Non-Potable Water Installation & Operation Instructions", [PDF] Amtrol Corporation 1400 Division Road, West Warwick, RI USA 02893 T: 800.426.8765 F: 800.293.1519 www.amtrol.com , retrieved 2016/06/06, original source http://www.amtrol.com/media/documents/extrol/9015183_06_15_EXTROL_IO.pdf

So before moving the expansion tank to the return side I'd contact the company for advice.

Keep in mind that the company offers a variety of expansion tank designs including a floor-standing model might let you locate the expansion tank where you have room, but piped to the supply side of the hot water piping loop.

Can I move the expansion tank and if so, where?

by (mod) - where to relocate the expansion tank

Russ,

Depending on the type of expansion tank you do have some latitude in where it is located.

You need to note the brand and model of your specific expansion tank, then review its installation and operation manual

We give links to some widely-used expansion tank manuals at EXPANSION TANKS, BOILERS

Shown here is a typical installation sketch from Amtrol's instructions for two types of expansion tanks shown.

Here are excerpts from those instructions.

Watch out: this information is given as an EXAMPLE - the instructions and requirements for your brand and model expansion tank may well differ.

Mount tank vertically only. Ensure the piping can support the entire weight of the tank when full of water.

Models SX-30V through SX-60V are floor standing and may not be hung from the piping.

Do not install the EXTROL on a dead-end pipe or wherever air can collect. This can cause corrosion and possible leakage

Install the EXTROL on the supply side of the boiler, on the suction-side of the heating circulator(s) (Figure 2).

See these

Boiler Expansion Tanks & Other Boiler Controls

• AIRTROL Installation Manual [PDF]
• AMTROL Extrol Expansion Tank Installation Instructions [PDF]
• AMTROL Extrol Expansion Tank Manual [PDF]
• B&G AIRTROL Expansion Tank Manual [PDF]

I can't find the expansion tank for my heating boiler

Just moved into an old house and the only pressure tank I can find is the one next to the well pump. Is it normal to not have an expansion tank or (obvious) relief valve anywhere? (Jan 5, 2016) Jim said:

Reply:

Thanks for asking, Jim.

It may depend on where you live and local custom, but most of the private homes I've inspected over the last 40 years did NOT have a hot water system expansion tank.

More likely it's a component people add when they're having trouble with the hot water system.

If your home heating system is by hot water, there will be an expansion tank protecting the boiler.

See FIND the EXPANSION TANK for help finding the expansion tank when you don't see one at the boiler itself

Jim said: maybe my system has no expansion tank?

The hot water heater is oil-fired and not used to heat the house. Maybe that's why there isn't one. The hot water takes a minute to reach the fixtures (especially upstairs), but the water is hot and pressure is not an issue.

(mod) said: expansion tanks found on all heating boilers but not on all domestic water heaters

You won't find a conventional hydronic (hot water) heating boiler installation with NO expansion tank anywhere as the system would not work properly and would be frequently spilling at the relief valve - an unsafe condition.

Thanks for the added detail; indeed, as I opined, for domestic hot water (for washing and bathing), most residential hot water heaters (calorifiers, geysers) don't have an expansion tank.

If you are not having a problem with leaks at the TP valve on the water heater you're probably OK.

See ATTIC & ANTIQUE EXPANSION or HEADER TANKS to see how older heating system hot water expansion was handled.

Expansion tank should be on supply side of the pressure regulator, ours is on the other side

We have two boilers (50 HP each) that supply the facilities heating including hot water through indirect tanks. I have decreased one of the boilers temperature to minimum. We have just began having call for in floor heat so demand on boilers is low. typically at night in-floor heat pumps will operate.

Daytime temperatures in Nova Scotia still reaching 20 degrees Celsius 68 F.

When you say add an expansion tank can you elaborate as the one specified is not readily available?

One question in regard to proper placement of Back flow preventer.

The literature I have read is that it should be on supply side of Pressure regulator.

Seeing ours was installed down stream from Pressure regulator would this be an issue in maintaining boiler pressure - (Sept 25, 2016) Dan

Reply: follow the instructions in the manual for your specific expansion tank

I would absolutely trust the manufacture's literature over urban legend.

It's always safest to give the manufacturer's technical support line a call to ask directly.

To download a free PDF copy of the installation / operating instructions for your (or almost any) boiler expansion tank

see EXPANSION TANK IO MANUALS & SIZING GUIDES

Shouldn't the expansion tank be installed before the circulating pump?

Great info. and much appreciated. I have learned a great deal about my hydronic system from this site.

It is time to replace the old bladderless expansion tank (hanging in ceiling) due to a leak.

The online calculators indicate the model SX-30V would be an appropriate replacement.

My system uses cast iron radiators, and the old bladderless expansion tank has a pipe routed from the 1 1/4" copper output pipe (after hydronic circulating pump).

The replacement is a stand model and I thought I read it should be installed before the circulating pump, and there should be an air vent and air separator installed. Is that correct?

Any guidance on this would be useful/helpful. I saw an online diagram, but it is confusing since my system is setup somewhat different. On 2019-01-21 by Javier

by (mod) - Yes - here's a link to the manual for installing your SX-30V Expansion Tank

Javier

Usually the expansion tank is located on the cold water supply side of the heating boiler.

For your expansion tank the IO manual shows it installed between the boiler and the circulator pump.

We give links to some widely-used expansion tank manuals

at BOILER EXPANSION TANK INSTALLATION & OPERATION MANUALS

There you'll see the typical locations recommended by the tank manufacturers.

Or download this:

Amtrol Corporation, INSTALLATION & OPERATION INSTRUCTIONS, EXTROL (R) HYDRONIC DIAPHRAGM EXPANSION TANKS IN-LINE & SX-SERIES [PDF] (06/15), Amtrol Corporation, 1400 Division Road, West Warwick RI 02983, Tel: 401-884-6300, Website: www.amtrol.com, retrieved 2016/05/10, original source http://www.amtrol.com/media/documents/extrol/9015183_06_15_EXTROL_IO.pdf

I expect you'll see that you've got a bit of latitude on tank location and for some expansion tanks, mounting position.

We excerpted the manual I just cited and included its illustration for your expansion tank right next to your question.

Below we also show the mounting location for the Amtrol EX-15 - EX-90 expansion tanks.

I have to empty our boiler's expansion tank every month - the relief valve spills; how far away can I put the new replacement tank I'm planning?

I have oil burner and I have to empty the expansion tank about once a month. I know it's full when the relief starts passing water.

It's an old tank that lay's on top of the heater. My question is if I install the new type what is the max distance can it be from the heater? Is 8' to far? - Tony 6/5/2012

Reply:

Tony,

Amtrol makes both thermal expansion tanks and hydronic expansion tanks used on heating and plumbing systems.

Amtrol's expansion tank installation instructions specify "Install the EXTROL on the supply side of the boiler, on the suction-side of the heating circulator(s) (see Figure 1)."

That is, the location is more critical than the distance.

Expansion Tank Repair or Replacement

Tip: See EXPANSION TANK LEAK REPAIRS where we discuss diagnosing and repairing leaks in boiler expansion tanks / compression tanks as well as relief valve leaks traced to problems with the expansion tank.

I keep having to add air to my Amtrol Fill-trol expansion tank! How do I replace it?

My Amtrol-Fitrol Model 110 needs to be topped-up w/air to every now and then to bring it up to 12 PSI. I figure it needs replacing.

There is a shut-off valve in line immediately before the tank.

Can I just shut off that (I guess water inlet valve) and swap out the old tank for a new one of the same model and manufacturer? Thanks. (Oct 16, 2014) Tom B.

Illustration: the Amtrol Filtrol expansion tank combines a traditional bladder-type expansion tank with an automatic water feed valve to control the heating boiler's base (when cold) water pressure.

Reply: When does an Amtrol Fill-trol expansion tank need repair or replacement?

Your system suggests that there is a leaky air valve or a burst or leaky internal bladder in the ekxpansion tank. If that's the case you'll need to replace the unit.

It is possible to replace a leaky bladder in some internal bladder tanks such as those used on water supply systems but for the smaller expansion tanks used on heating systems such as the Amtrol Extrol, bladder repair is not possible.

If the bladder is leaky on an Extrol tank, the tank needs to be replaced.

And yes, you can close the shutoff valve, replace the Amtrol Filtrol assembly,

and then,

if the amount of air entering the boiler system during that repair is quite small, and provided there are automatic air vents installed at the boiler and elsewhere on your system, you may not need to take an extra step to remove air from the boiler and its piping.

If you don't already have the installation and operation manual for your Amtrol Fill-Trol Model 110, download this copy from Amtrol or contact us if you have trouble with their link.

AMTROL FILL-TROL INTALLATION & OPERATION MANUAL [PDF] (2019) (at Amtrol) - Models FT-109 through FT-111 For Use In Closed Hydronic Systems Only - local copy saved as Amtrol-Filltrol-IO-Manual.pdf

Excerpt: FILL-TROL® is a combination of an EXTROL® expansion tank and a specially designed automatic fill valve. Together, they manage water expansion and provide make-up water to provide satisfactory heating system.

Below: Amtrol's installation instructions for the Fill-Trol explain that the service cap on this tank is normally white in color. If the cap changes color the bladder is leaking and the tank assembly needs to be replaced.

However the company warns that you cannot rely only on the cap color to determine if the tank needs replacement.

So from your description it sounds as if your tank needs repalcement regardless of the cap color.

- Daniel Friedman

What are the proper repairs to an expansion tank, air vent, pressure reducer?

I am purchasing a house with an oil-fueled hot water boiler (NewMac NBR-2002).

During an inspection of the system, it was determined that the expansion tank and the automatic air vent needed to be replaced, and my technician also indicated that the pressure reducing valve would likely need to be replaced.

Instead of crediting me the cost of those repairs, the owner instead had another heating company replace the expansion tank and the air vent, and that technician declared that the pressure reducing valve was working just fine.

My technician told me that one has to run the system for as long as a week to know whether that valve is actually working properly.

There is clearly a difference of opinion here. Comments? By the way, we live in an area with very hard water. 11/20/2014 Anonymous

Reply:

Anon:

If the water feeder-pressure reducer valve has failed you would probably see the boiler over pressurized and leaks at the relief valve. Maybe your tech was being safe (spending other people's money to reduce his risk) or maybe he or she saw something not reported here.

But the seller's repair was a reasonable step. For the valve to also be a problem would at this point be a double fault - less likely. If the repair already done was not effective you should see that as excessive boiler pressure - typically in 1-5 days. Look again.

Is it safe to remove and replace an old steel expansion tank with the newer type? Which is better?

is it safe to remove the horizontal type tank and replace it ? Is the old type better? is it ok to let the valve relieve the pressure and not have a tank at all? - Anon 9/11/11

Reply:

Anon, you can usually replace an old bladderless expansion tank with a much smaller internal diaphragm tank, as we describe above.

The new tank will be smaller yet can handle the same job.

Newer internal-bladder heating system expansion tanks such as the Fill-Trol® Diaphragm-Type Expansion Tank have the advantage that you don't need to periodically drain the tank to re-charge its air.

In choosing the size of a heating system expansion tank, the service technician will consider the size of the building being heated, or more accurately, the volume of water in the boiler and heat distribution piping & radiators.

Steam boiler had two expansion tanks - was it ok to remove one? Now we have no heat.

I am a home owner, i had a plumber switched and installed a steam heater in the first floor. When he saw my oil boiler that had two Expansion Tanks, he said it would work more efficient if he removed one on the two.

He removed a green horizontal one at no charge, but took the Expansion Tank with him.

Now that same steam heater he installed does not warm up at all. Is this because he removed one Expansion Tank.
please help - Laura 10/30/11

Reply:

Laura: steam boilers won't use an expansion tank, not normally, as the boiler is making steam and open to the atmosphere up through the radiators and steam vents.

Usually on a modern hot water (not steam) heating system you wouldn't need two expansion tanks, certainly not if one of them is a new internal bladder type.

So, recognizing that I can only guess from afar, it sounds like two different problems.

There are some steam heat systems that use steam to distribute heat to upper building areas and use hot water from the same boiler to circulate through hot water radiators or baseboards in a lower building area. Maybe that's what you've got ?

Call your heating service company and politely, tell them that after service you have no heat, and ask the service manager to send an experienced steam heating technician to your home to sort out the trouble.

Boiler Expansion Tank Size FAQs

How to choose the right size of expansion tank

Expansion tank sizing: In a very large old home, there is a huge boiler(size of a small car) and an old style expansion tank in the rafters. The tank recently started leaking, so I'd like to replace it with the newer bladder type.

I understand for sizing calculations, you need to take the system volume, temperature differential, etc. into account. But with a house so large with dozens of radiators & seemingly miles of piping, I can't begin to imagine how you could calculate the total volume.

I'sn't there a way to make this determination using the size of the old expansion tank? Its 12" x 60", so about 30 gallons. Thanks for the help. Steve said:

Reply:

Steve,

Yes indeed. The boiler expansion tank is sized based on the total volume of water in the hot water heating system.

Please see complete details at EXPANSION TANK SIZING GUIDE