Hot water heating system expansion tank / compression tank installation, troubleshooting, repair questions & answers. :

This article series explains how to identify, inspect, install, repair, or service heating boiler expansion tanks: here we explain the function of expansion tanks on hot water (hydronic) heating systems.

Heating Boiler Expansion Tank FAQs

These questions & answers about expansion tanks used on heating boilers were posted originally

at EXPANSION TANKS, BOILERS - topic home - be sure to see the explanation and boiler expansion tank installation, diagnostic and repair advice given there.

On 2018-07-29 by (mod) - which valve drains the expansion tank

Roncas

If the drain valve you see is on the boiler itself that's not going to drain the expansion tank.

Keep in mind that not all expansion tanks are designed to be drained.

If your expansion tank uses an internal bladder then it's not able to be drained.

If your boiler uses an older style bladderless expansion tank like the one shown just above, there is usually a tank drain valve mounted near one end - yellow arrow marked DRAIN in my photo. This might be a special valve designed to allow air to enter the expansion tank while water is being drained out.

See details at EXPANSION TANK DRAIN & AIR RE-CHARGE.

On 2018-07-28 by roncas

trying to bleed drain the expansion tank the only valve I see that has a hose thread is in front and doesn't seem to be near the expansion tank

On 2018-04-21 23:23:20.374251 by (mod) -

It sounds to me as if there's a leak where there should not be one. I hope you turned off the heater and called your heating Service Company for prompt repair

On 2018-04-20 15:41:18.155246 by Paul

My expansion tank is hissing load what do I do

On 2018-03-30 by Jeff

My boiler makes a bang sound and the relief valves goes off almost every day.

When boiler is off no pressure in lines

What causes this

On 2018-02-26 by (mod) - noises from the expansion tank

Grace

Normally the expansion tank on a hot water heating system is silent.

There are several heating system noises that might show up at an expansion tank including

- rattling from inadequate support - older type bladderless ceiling-mounted tanks with loose strapping

- thermal expansion, clanks and thunks as temperatures change

- water hammer noises that happen to be amplified by the expansion tank, when a zone valve opens or closes or a circulator starts or stops.

- nearby heating pipe gurgling sounds or "banging noises" due to air in the system (air purge valves are not working or there is an air-leak into the system

- banging sounds traced to sediment build-up (mineral deposits, rust, debris) and on occasion partial clogging in the boiler itself or circulator or zone valve or piping

- actual boiling water -

Watch out: this is abnormal in a hot water (hydronic) heating system.

Normally water temperatures do not exceed 200 degF. Check the aquastat settings and the boiler temperature gauge. Boiling water will typically cause the temperature/relief valve to open to relieve temperature and pressure.

So if your boiler is truly boiling and the TPR valve is not opening your system is doubly unsafe: it's too hot AND a safety device is not working. I would turn such a system OFF and call for repair.

Boiling water is of course normal in a steam boiler.

- boiler water pressure is normally between about 12 psi when the boiler is cold and under 30 psi when the boiler is hot. Abnormally low boiler starting pressure might encourage boiling water - an abnormal condition and not one I've encountered.

See HEATING SYSTEM NOISE DIAGNOSIS - https://inspectapedia.com/heat/Heating_Noise_Diagnosis.php for our complete catalog of noises traced to heating equipment.

Also see EXPANSION TANK LEAK REPAIRS at https://inspectapedia.com/heat/Expansion_Tank_Leak_Repairs.php

On 2018-02-2 6 by Grace

My expansion tank make boiling water noise what cause it

On 2018-02-16 by (mod) -

Sandra

When an expansion tank and relief valve have been replaced, if there is then boiler water leaking out of the system there is a problem to be diagnosed and fixed - possibly one that was not apparent to the original service technicians in the first place.

Stating that "... the pressure relief valve had just let out a little water after their boiler service. " is not reasonable nor acceptable UNLESS that water was released because someone tested the valve by lifting its test lever.

Otherwise water should not be coming out of the valve.

Or of course there could be a leak somewhere else that wasn't found.

There are other causes of TPR valve leaks and boiler leaks, but I can't speculate further - it'd be too much arm-waving.

Invite the service manager to send an experienced crew to the home to finish the job properly. Politely and calmly so as to see if you can get them on your side.

On 2018-02-15 by Sandra - why would TPR valve fail during boiler service?

I had my oil burner annual service in October.

The boiler had been operating earlier that day as the weather had already become cold. It was operating fine prior to service. When the service people were packing up I went into the basement to check in.

I was noticed a small pool of water on the floor, maybe 12 inches in diameter or a little larger. When I looked over at it one of the technicians said that they had just noticed it too and they had no idea why it was there.

They said they double checked everything and could find no reason other than maybe the pressure relief valve had just let out a little water after their boiler service.

They thought I shouldn't be concerned and that they didn't believe it would continue to leak. They acknowledged that it had not been leaking before they began their work and so they really didn't think there was any problem. They left and the leak got worse and worse over the next several days. I had to call them back to the house as it was really letting out a lot of water.

I was at work when they came back to the house and I just received a bill that says they replaced the pressure relief valve as well as the expansion tank due to expansion tank failure.

My question is this- Why would this suddenly fail at the end of their servicing my boiler.

We had absolutely no leakage or other issues until then.Could they have made some mistake that caused this to happen? It seems far too much of a coincidence that it would just suddenly fail at their visit and they hadn't noted any issues at all when servicing the boiler.

On 2018-01-17 by (mod) - Boiler water might leak into a tankless coil IF

Mag

Boiler water might leak into a tankless coil IF boiler pressure is above the house water system pressure.

A residential heating boiler won't get above 30 psi since at that pressure the TPR valve would open and spill water and pressure and temperature.

Home water supply systems can indeed sometimes be lower than 30 psi, such as on a private well system at which the water pressure ranges between 20 psi and some higher cut-off pressure (typically 40 psi). A home water system connected to a municipal supply is usually above 30 psi but not always and not in all locations.

So yes, it's possible.

The leak can be in either direction - into the coil or out of the coil.

See TANKLESS COIL INTERNAL LEAKS INTO the BOILER https://inspectapedia.com/plumbing/Tankless_Coil_Leaks_Into_Boiler.php
where I'll post your question and this reply

On 2018-01-16 by mag

Thank you for the valuable information provided on the site. Regarding leaking from or into the heating coil I believe I have a situation in which boiler water is entering into the coil, i.e. there was a strong smell of antifreeze, but fortunately it was food grade type.

Apparently all antifreeze has been exhausted. I've continued to use the furnace to heat the house and provide hot water. In this scenario where boiler water is entering coil I've assumed the greater pressure is outside the coil, in the boiler water side. What would cause boiler to over pressurize?

I realize I should replace the coil if it has leaks, but is it possible that the boiler water is entering house hold hot water via the expansion tank? Many thanks for your help.

On 2017-12-28 by (mod) -

Tim,

I apologize that we cannot always answer immediately. With thousands of readers sometimes we get a bit behind on Q&A.

For the case you describe there are two diagnostic procedures that I recommend

1. Cold radiators - COLD HOT WATER RADIATOR or BASEBOARD https://inspectapedia.com/heat/Cold_Radiator_Repair.php

Typically, after ruling out a problem at the thermostat or its wiring, there will be a control or relay or circulator problem if the circulator is not running, OR the system is air-bound.


2. boiler no-heat problems DIAGNOSE & FIX HEATING PROBLEMS-BOILER https://inspectapedia.com/heat/Heating-Boiler-Diagnosis.php

Other hot water heating snafus diagnosed here starting with some basic checks.

On 2017-12-28 9 by Anonymous

Boiler is hot, radiators are cold, circulating pump is working fine. What' wrong ?

On 2014-03-26 by (mod) - horizontal vs. vertical mounting position of bladder type expansion tanks

Anon,
The Amtrol company's installation instructions for the Extrol 30 does not mention horizontal vs. vertical mounting position for the device, but the installation instructions do include a sketch showing the unit in a vertical position.

The instructions also include this line "Do not place the EXTROL on a dead-end pipe.

Air can collect in the EXTROL, causing internal corrosion and possible leakage."

Which I take to warn you that *any* installation that might allow air to collect in the device could cause corrosion and leakage.

Watch out: That is, in my opinion, precisely the risk that you might face if your unit is mounted horizontally.

On 2014-03-26 by Anonymous

I have a system 2000 gas fired furnace that has a Extrol 30 that is mounted sideways instead of hanging down. It has waterlogged for a fourth time in the last 20 years and about four years ago was the last time until now.

Does the tank being mounted horizontally instead of vertically have an effect on the life of the bladder? I don't remember ever having to replace one in any house I lived in until I moved in here. Rick Bouchard globe56@myfairpoint.net

On 2014-03-03 by (mod) - for the operation of the Extrol expansion tank itself an air vent and purger are not required

Anon: for the operation of the Extrol expansion tank itself an air vent and purger are not required, but for proper functioning of the heating system where the Amtrol Extrol Expansion Tank No. 30 is installed, indeed an air purger and vent are needed. Here is what the company says in the installation instructions for their Extrol expansion tanks:

The EXTROL is installed on the supply-side of the boiler system. Its sealed-in air pre-charge prevents water from entering the tank until the system pressure begins to rise.

As the water temperature rises, water enters the EXTROL.

As the system cools, the diaphragm is forced downward. Water is expelled from the EXTROL, back into the heating system.

Although the EXTROL does not have to be installed at the base of an air purger, this installation is recommended to reduce air in the system and provide a compact installation. Some method of air elimination is required to ensure an oxygen-free system.

On 2014-03-03 by Anonymous

did "Amtrol Extrol Expansion Tank No. 30" need air vent and air purger

On 2013-02-24 by Rosemary

I have a 50+ year old hot water boiler system. The piping runs through a concrete slab floor to baseboard heating units. In the past few weeks I have heard a pretty significant, intermittent trickling/running of water around my boiler but can't pinpoint where.

No visible water on the outside of the boiler. I also hear the a singe-like sound of water hitting a hot surface. I can't find the pressure gauge (most of the piping to the boiler is inaccessible to me) so don't know what the pressure is. Ideas what this might be? Thanks!

On 2013-01-29 Bill Poulsen

Just wanted to let you guys know that you have teh best and most helpful information for this kind of stuff anywhere on the web. I've had issues with my hot water system where the relief valve was releasing water quite often, and now understanding the operation and mantenance for the expansion tank you have solved my problems!

Thanks for the help!

On 2013-01-27 18:19:51.113658 by Tom Leahy

My Extrol expansion tank pressure is reading zero. Cannot get hot water from the basement to top floor. Is the expansion tank defective? Could it be a valve?

Thank you for your help.

On 2013-01-25 10:21:11.975883 by john spinosa

3 zone system I bring the pressure up to 12#s in a few days it drops to 7#s and I can hear air in the system. How could air get in the system when it has pressure and where is the water going. I don't see any leaks

On 2012-12-26 07:39:50.658594 by Anonymous

Heating system contains a : Hot water Boiler , Primary Pumps, secondary Pumps,Heat Exchanger and finally a secondary pumps for each building with radiators , we have problem that the pressuré gages at at Discharge Head indicate (8 bar) and gage at Suction Head (6 bar),(the pumps run at full load 50 Hz), While the design head is (35 m), expantion tank is installed put still we have high pressure,
bearing in mind that we make balancing for water flow for th system.

On 2012-12-20 15:21:46.360267 by Steve

Can the bladder in a expansion tank detearate and work it way into the hot water lines.

On 2012-12-10 05:14:39.764036 by Bert

While refurbishing a property thieves took removed copper heating and plumbing supply lines draining out system. After reading your articles I understand the basics of my system. Do we just refill it and be sure to get the air out of the lines before turning the burner back on.

They drained the system when it was still operating so the circulation pump may be damaged as we didn't discover the damage until a few days later.

On 2012-12-07 00:06:01.806493 by (mod) -

Elvin,
Draining an expansion tank is not a repair for a boiler that won't run.

See the link near page top

DIAGNOSE & REPAIR HEATING BOILEr

On 2012-12-06 19:57:09.684902 by Elvin Madera

When turn on the boiler still work a few minutes and go off, if I drain the and still drain the water the boiler still working, whats the matter?

On 2012-12-04 22:13:41.258606 by Dale Binsberger

How do you drain a bladderless expansion tank in a hydronic oil heat system that has no pressure regulator valve or expansion tank isolation valve? It does have the newer air bleed drain valve installed on the bottom of the tank.
Thanks,
Dale

On 2012-11-29 01:26:44.321602 by Josh

I'm having trouble pushing water into my third floor radiators. I noticed that the pressure is pretty high and that the valve between the expansion tank and boiler is shut off. Should this valve be open? Is it safe to open it? Should I turn the furnace off first and let it cool down?

On 2012-11-17 01:04:22.804410 by John OHare

Thank you for this informative information. Many articles just mention the expansion tank with bladders but I have an old bladderless system and I was not sure if I should let the water out The over pressure valve was periodically going off. Thanks again, I believe you solved my problem.

...

Continue reading at EXPANSION TANKS, BOILERS - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• EXPANSION TANKS, BOILERS - home
  • AMTROL's EXTROL®, the FILL-TROL®
  • ATTIC & ANTIQUE EXPANSION TANKS, HEATING
  • BOILER DRAIN DAMAGES EXPANSION TANK
  • EXPANSION TANK AIR VALVE LEAKS
  • EXPANSION TANK DIAGNOSIS
  • EXPANSION TANK DRAIN & AIR RE-CHARGE
  • EXPANSION TANK IO MANUALS & SIZING GUIDES
  • EXPANSION TANK LEAK REPAIRS
  • EXPANSION TANK PRESSURE ADJUSTMENT
  • EXPANSION TANK SIZING GUIDE
  • EXPANSION TANK WATERLOGGING CAUSES
  • EXPANSION TANK WON'T DRAIN
  • FIND the EXPANSION TANK
  • HEADER TANKS
  • RELIEF VALVE LEAK DUE TO EXPANSION TANK
  • TANKLESS COIL INTERNAL LEAKS INTO the BOILER
  • THERMAL EXPANSION of HOT WATER
  • THERMAL EXPANSION TPR VALVE LEAKS
  • WATER PRESSURE TOO HIGH: DANGERS

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EXPANSION TANKS, BOILER FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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