Hot water heating system expansion tank / compression tank leaks: troubleshooting, repair questins diagnostic questions & answers:

Reader questions about diagnosing leaky TPR valves, leaky expansion tanks, hot water system pressure problems & explanations of how expansion or compression tanks actually work on hydronic heating systems help diagnose problems with these components.

This article series provides a heating system expansion tank (compression tank) troubleshooting & repair guide.

FAQs on Leaking Heating Boiler Expansion Tanks:Troubleshoot, Understand, Fix

These questions & answers about the expansion tank or compression tank used on hot water heating boilers were posted originally at EXPANSION TANK LEAK REPAIRS. Please be sure to review the diagnosis and repair advice given there.

The photo at page top shows a traditional steel bladderless compression tank on a hot water heating systems. Most techs and owners call these "boiler expansion tanks".

At left is a modern Extrol(R) bladder-type heating system expansion tank.

[Click to enlarge any image]

On 2019-01-21 by (mod) - should the expansion tank be installed ahead of the circulator pump?

Javier

We give links to some widely-used expansion tank manuals

at EXPANSION TANKS, BOILERS - home inspectapedia.com/heat/Boiler-Expansion-Tanks.php

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

I expect you'll see that you've got quite a bit of latitude on tank location.

On 2019-01-21 by Javier

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 2018-10-28 by (mod) - /heat/Boiler-Expansion-Tanks.php

Alex

There are two distinct types of expansion tanks on hydronic heating systems.

1. Tanks that use an internal bladder such as made by Amtrol/Extrol. Those might have a slight pressure adjustment at time of installation but otherwise never need service.

2. Tanks that do not use an internal bladder. Those may become waterlogged over the course of a heating season or two. At annual service the tech drains the water from the expansion tank, allowing air to enter it at atmospheric pressure - extra air is NOT pumped into the tank.

When a type 2 expansion tank (also referred to as boiler compression tank) has been drained and is air-filled, and when its isolation valve is then opened, the heating system's water, contained in the boiler and piping, enter the tank under the normal pressure of the heating system.

Typically, depending on a few variables like building height and heating system temperature, the pressure will be somewhere between 12 psi and just under 30 psi.

Do not pump extra air into your expansion tank - nor is there a fitting permitting you to do so.

On 2018-10-28 05:52:11.008637 by Alex Nagy

What happens if I let the air out the tank on my heating system. can I just pump the tank up with air again

On 2018-08-03 by (mod) - where to locate 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 - home https://inspectapedia.com/heat/Boiler-Expansion-Tanks.php

Below 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]

On 2018-08-01 00:10:33.802078 by Russ

The expansion tank is in a place where I need to put a new tub, can I move the tank ? Where?

On 2018-03-02 16:30:07.971980 by jorge

I have a large steel expansion tank, bladderless, with a sight glass on it and a pressure valve.

I don't belive it's pre-charged probably atmospheric pressure to begin with. The sight glass is full of water and the pressure located at the top of the heating system and on top of the tank is 20psi. That doesn't sound right to me. What do you think.?

On 2018-02-26 13:10:35.381522 by Grace

Is it normal to hear water boiling noise in expansion tank when boiler click on

On 2018-02-23 23:10:33.705605 by (mod) -

Not exactly seating itself it shouldn't leak from the get-go. But you could try depressing the pin and letting a little water out and then seeing if it stops.

That might wash a little dirt off the valve seat. Also check carefully to see exactly where the water is coming out. Also if you can pick up a tire valve repair tool you can check that the stem is screwed all the way in to the valve base.

On 2018-02-23 20:36:04.856097 by VinSez

DanJoe... I did replace the entire Taco Air vent. I guess it's possible that the new one was/is defective. Gould it have been due to new replacement the valve needed to seat itself?

Also, wont't the air vent above the epanio tank do the job?

On 2018-02-23 17:40:33.104751 by (mod) -

All of that sounds correct. However if your air vent is leaking most likely that's not a pressure problem there. Instead it's that the Schrader valve core in the vent has failed or is debris clogged. You can replace the core but it's probably smarter just to replace the whole bleeder valve. You want to be able to leave that count loose, otherwise the valve can't automatically release on wanted excess air from the system.

If you don't release unwanted excess air from the system your heat could become air bound and you simply won't have heat in the occupied space

On 2018-02-23 14:42:09.393150 by VinSez

Tapped on the expansion tank and it sounds hollow, so I don't believe the tank is waterlogged.

Was considering adding some air? It's now been three days and no overflow from the TPR valve or the air vent, albeit, I've closed the cap on the vent. It never seemed to be a pressure issue, however, temp risen to a bit over 200 degrees - - it's now at about 195.

When you speak about the 'cold start temp' I assume you mean that on the front temp gauge?

If so, it is at about 10 PSI when cold. I am going to open the replacement air vent and watch it when the boiler goes on; otherwise, I have no idea what caused the second leak

On 2018-02-22 23:33:52.043818 by (mod) -

Vince,

If you're getting recurrent leaks at an air vent, the air vent is defective or improperly installed.

If you're seeing leaks at the relief valve then ... it depends. The problem could be a waterlogged expansion tank in which case you also want to see

THERMAL EXPANSION TPR VALVE LEAKS https://inspectapedia.com/plumbing/Water-Thermal-Expansion-Leaks.php

OR something else - see RELIEF VALVE LEAKS https://inspectapedia.com/plumbing/TP_Valve_Leaks.php where we catalog causes of TPR valve leaks

As long as the system pressure is below 30 psi (at which the TPR is supposed to open) and the temperature below 200F in the boiler, the leaks at the relief valve are not due to boiler aquastat settings.

If pressure is abnormally high check the cold start temperature to be sure it's below 12-15 psi. If that pressure is too high (when the boiler is cold, you'd look for a defective pressure reducer or water feeder)

On 2018-02-22 23:03:22.896460 by VinceSez

STUMPED...I have a 1990's Burnham boiler, with Amtrol (Extrol) Model #30 expansion tank, a Taco air vent directly above the expansion tank, and another one below (before Relief Valve). Recently, had a leak from the old, lower air vent causing a wet finished basement.

I had an HVAC plumber stop by and he had me replace the lower Taco vent. Two days went by no problems, then another leak situation, seemingly caused be the "new" air vent. I closed the cap tight and since have not had a problem.

However, before having a new carpet installed I want to be sure I've gotten to root-cause? During both leaks, the Pressure Relief valve sent some water into a bucket I have below it; about 3" of water in the pail; most of the leak came out of the air vent, I believe?

The pressure read on the front of the boiler shows it is operating at about 13 PSI and the temp, upon boiler fire goes up to about 200 degrees.

I adjusted the Aquastat setting to: Low=160, High=190, Diff= 25;

this seemed to lower the upper end pressure to about 195 degrees.

I had another HVAC guy tell me that he would replace the Pressure Relief Valve, the Expansion tank, and one other item (without seeing the system) at a cost of $500 - - which knowing the price of the parts is ridiculous!

Since I don't have any ;leaks or output from the Relief Valve since closing the lower air vent cap, I don't know what to think? The entire system is aprox. 25 years old, but has been working fine...

CAN YOU PLEASE PROVIDE SOME INSIGHT INTO WHY I MAY HAVE HAD A LEAK IN THE FIRST PLACE? WHY THE NEW AIR VENT ALSO LEAKED? AND, HOW CAN I BE SURE I'VE FOUND ROOT-CAUSE?

On 2018-01-14 20:22:39.556112 by (mod) -

Nathan

I cannot be smarter than an onsite expert, but it seems to me that if the cause of the TPR discharging were truly that the expansion tank on your boiler were too small, and considering that it has been in place 15 years, surely the TPR valve would have been discharging for fifteen years.

More likely the expansion tank is waterlogged.

Expansion tanks that do NOT use an internal bladder can be drained and re-filled with air as a standard service procedure to stop the problem. If your expansion tank is a type that uses an internal bladder, then yes it most likely needs to be replaced. Replacing a TPR valve that has been leaking is generally a safe additional step as mineral scale and deposits can make a leaky TPR valve unsafe.

On 2018-01-14 19:16:09.591761 by Nathan

My pressure relive Val, exiting my furnace has triggered. I'm told that it's because my expansion tank of 15years is to small. And needs to BE replaced along with the Val.
At the reduced price of $500.00

On 2017-07-12 19:41:49.172173 by (mod) -

Extrol

It would be quite odd for an expansion tank to prevent the delivery of hot water; all the tank is doing is sitting attached to the hot water piping acting as a "spring" to absorb temporary increases in water pressure due to heating of the water when no water is being run - thus avoiding a risk of causing a temperature/relief valve on the water heater to open.

If you tell me more about why you suspect the expansion tank perhaps I can comment further.

To diagnose loss of hot water I'd start at this article:

WATER HEATER PROBLEM DIAGNOSIS at https://inspectapedia.com/plumbing/Water_Heater_Diagnostics.php

On 2017-07-12 18:55:15.344951 by Extrol Model 15 - No Hot Water

Hi Please help! We have this hyrdronic expansion tank and need to figure out why we have no hot water in our house. Recently, i noticed it wouldn't last very long then there was just none.

Thanks,

DB

On 2017-04-04 00:17:50.116301 by (mod) -

Sounds as if your water has a sulphur content. Have you had it tested?

Search InspectApedia.com using the box above for SULPHUR ODORS in WATER for details.

On 2017-03-30 03:54:28.203095 by Bill

Thanks for the interest in this. The odor from the expansion tank water is exactly the same that we smell at times in our drinking water. If the water in the expansion comes from the heating system water (which contains antifreeze), then there may a tankless coil leak scenario.

I have a water sample out to a lab to test for antifreeze, among other VOCs. I am going to have the boiler/tankless coil checked. We are using bottled water until we figure this out. I will keep you in the loop, if you want, since this may be unusual.

On 2017-03-29 19:01:45.093247 by (mod) -

Bill

You should not have to drain the expansion tank more than once. It's normal for the boiler water to be smelly - the same water cycles around in the boiler and piping system for years.

I'm unclear what you mean by "burner pressure at 15 lbs" - the burner doesn't have a water pressure. You probably meant boiler pressure - and yeah, 15 psi would be in normal range. And 42 psi is normal range for a building water supply system pressure.

I don't consider the smell an issue unless you thought you were getting the same odor from your building water supply (as opposed to drainage from the boiler).

Water treatment on heating boilers is important on commercial systems (for corrosion protection) and of course on steam boilers that keep taking in new water. It's much less common on residential boilers. Antifreeze is used in some residential boilers - so if there were a tankless coil leak that happened to find that unlikely scenario

I described before (boiler leaks into building water supply) that would be dangerous unless food-grade antifreeze were used. As I said, if a coil leaks the more likely scenario is that boiler pressure keeps creeping up and the TPR valve leaks.

On 2017-03-29 03:08:19.860123 by Bill

Thanks for the info...very helpful. Drained the expansion tank several more times. Again, same smell from that water as in the potable water...only much stronger. Also, getting brown sediment in the tank water. Maybe iron bacteria growth since we have been getting small pieces of metal like grit in the potable water along with the brown sediment in the tank water (staining the slop sink). Maybe should pull the submersible pump up some.

Checked burner pressure at 15 lbs. when firing. Well water tank pressure at 42lbs. Does not suggest a coil leak but asked to check water for antifreeze VOC as well as iron bacteria. Will write back when we figure this out. Thank again

On 2017-03-29 by (mod) - if a tankless coil is leaky which way does the leaking water move: into the boiler or into the building water piping?

Bill

You should not have to drain the expansion tank more than once. It's normal for the boiler water to be smelly - the same water cycles around in the boiler and piping system for years.

I'm unclear what you mean by "burner pressure at 15 lbs" - the burner doesn't have a water pressure. You probably meant boiler pressure - and yeah, 15 psi would be in normal range. And 42 psi is normal range for a building water supply system pressure.

I don't consider the smell an issue unless you thought you were getting the same odor from your building water supply (as opposed to drainage from the boiler).

Water treatment on heating boilers is important on commercial systems (for corrosion protection) and of course on steam boilers that keep taking in new water. It's much less common on residential boilers.

Antifreeze is used in some residential boilers - so if there were a tankless coil leak that happened to find that unlikely scenario I described before (boiler leaks into building water supply) that would be dangerous unless food-grade antifreeze were used.

As I said, if a coil leaks the more likely scenario is that boiler pressure keeps creeping up and the TPR valve leaks.

On 2017-03-29 by Bill

Thanks for the info...very helpful. Drained the expansion tank several more times. Again, same smell from that water as in the potable water...only much stronger. Also, getting brown sediment in the tank water.

Maybe iron bacteria growth since we have been getting small pieces of metal like grit in the potable water along with the brown sediment in the tank water (staining the slop sink). Maybe should pull the submersible pump up some.

Checked burner pressure at 15 lbs. when firing. Well water tank pressure at 42lbs. Does not suggest a coil leak but asked to check water for antifreeze VOC as well as iron bacteria. Will write back when we figure this out. Thank again

On 2017-03-28 by (mod) A heating boiler expansion tank water may smell from these sources:

A heating boiler expansion tank water may smell from boiler treatments, antifreeze, or just old heating water that may contain bacteria, rust, etc.

Boiler water could, in theory, leak into the building's potable water supply when a tankless coil is installed in the boiler, and IF the tankless coil has a perforation or leak. But ONLY when the boiler pressure is higher than the building's water supply pressure.

That is not normally the case. Normally a residential heating boiler ranges from about 12 psi (cold) to under 30 psi (hot) while house water pressure typically is above those levels.

(But not all the time, since on a private well system some pressure switches "cut in" at 20 psi).

But here's a critical clue to the presence of tankless coil leaks:
As usually, for at least part of the time, the house pressure is higher than the boiler internal pressure, if there is a coil leak water will leak INTO the boiler, raising its pressure above normal, showing up as relief valve leaks at the boiler or as abnormally high pressure readings on the boiler pressure gauge.

Search InspectApedia.com using the search box just above to find our article on TANKLESS COIL LEAKS for complete information.

Thanks for asking, Bill.

On 2017-03-28 by Bill - I drained my expansion tank and the water had a very strong chemical smell.

I drained my expansion tank and the water had a very strong chemical smell. I have that same smell in my potable well water supply (being tested). Is it possible that the antifreeze in my heating system is bleeding into the potable hot water supply within the tankless coil in the burner (there is no hot water heater)?

On 2017-03-13 by (mod)

See https://inspectapedia.com/heat/Expansion_Tank_Leak_Repairs.php where this question and reply are already posted

On 2017-03-13 by Anonymous

The valve on the top of the expansion tank is dripping water.

On 2017-03-02 by (mod) - should water be in the expansion tank?

It's normal for there to be water in the bladder in the lower portion of the tank. That ought to give a different sound when tapping there.

On 2017-03-02 by cliff

clh10@msn.com have a 4gal honeywell expansion tank w/butyl membrane above my boiler/furnace. was told to tap on it to give me an indication as to whether or not it needs to be replaced. when i tap on top half i get a ping, tapping on bottom half gives me a solid thud. is this normal?

On 2017-02-15 by (mod) - should there be air in the expansion tank?

Yes, Anon. If there were no air in the expansion tank there would be nothing that could be compressed in the tank (water is not very compressable).

Without that "spring" of compressed air to absorb an initial pressure increase in the system when the water is heated, pressure would cause unsafe leaks such as at the pressure relief valve.

On 2017-02-15 by Anonymous

Is there supposed to be air in the expansion tank or holding tank on a boiler system

On 2017-01-07 by (mod) - a dripping relief valve is unsafe and needs immediate attention

A dripping relief valve is unsafe. The problem could be a waterlogged expansion tank, over pressure in the system, over temperature in the system, a defective TP valve, or something else.

If your tankless coil is leaking into the boiler that'd cause overpressure. Check the pressure gauge to start.

Watch out: failing to fix a leaky relief valve risks a BLEVE EXPLOSION - search Inspectapedia.com to read details.

On 2017-01-07 by cliff

just left question on water valve drip forgot to include it is oil fired boiler furnce

I have a boiler furnace that heats water both for heating and domestic use. I just took notice that the water relief valve with pipe to floor is slowly dripping. good size wet spot on concrete floor. The drip is from inside if the pipe running to floor, nothing wet where valve is at top side of furnace.

I has a Honeywell Thermal Expansion Tank with Butyl membrane. Never saw it leak before. The furnace and everything around it was replaced in the early 2000's. Anything wrong or is this normal?

On 2016-12-22 by (mod) - If your expansion tank does not include and air adjustment valve, then the pre-charged pressure is probably not adjustable.

John,

If your expansion tank does not include and air adjustment valve, then the pre-charged pressure is probably not adjustable.

As long as the tank is the correct size for your system, and your boiler pressure when cold is at 12 PSI, and your boiler pressure when the boiler is hot is below 30 PSI, then the system should work correctly.

On 2016-12-22 by John

So, novice here - hydronic expansion tank died, rusted through (old). I have a new one - got the right size, etc, no worries there.

The furnace reducing valve is 12psi; the furnace psi shows 20 when it's cranking out hot water. How much pressure should the expansion tank have, and what can I do if it's already installed but overpressurized?

Thanks!!

On 2016-11-20 by (mod)

Steve your question on boiler expansion tank sizing is online in a detailed article I'll post

at EXPANSION TANK SIZING GUIDE

Question: 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.

Question: New steam heater installed for first floor; old boiler had two expansion tanks - was it ok to remove one?

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 ?

Question: 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.

Question: 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:

We will try. 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.

...

Continue reading at 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, 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

Suggested citation for this web page

EXPANSION TANK LEAK REPAIR FAQs-2 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 HEATING BOILERS

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