Boiler Expansion Tank Leak Repair FAQs-2

Q&A fix leaky or water-logged boiler expansion tank

Boiler Leaks: Expansion tank vs relief valve vs air vent vs boiler pressure

If my relief valve spilled is it because the expansion tank is too small?

My pressure relief Valve, exiting my furnace has triggered.

I'm told that it's because my expansion tank of 15 years is to small. And needs to be replaced along with the Valve.

At the reduced price of $500.00 On 2018-01-14 by Nathan

Reply by (mod) - recommended inspection & repair steps & parts

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.

Trouble finding cause of boiler leaks: do I need a new expansion tank?

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 2018-02-22 by VinceSez -

by (mod) - Boiler pressure OR a bad air vent or relief valve all can cause leaks: check boiler pressure

Vince,

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

See AIR BLEED VALVE LEAK REPAIR FAQs

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

OR something else - see RELIEF VALVE LEAKS 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)

by VinSez - Tapped on the expansion tank: sounds empty

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

by (mod) - air vent leaks are not a boiler pressure problem; replace the air vent

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

by VinSez - I replaced the air vent; new one leaked.

DanJoe. I did replace the entire Taco Air vent. I guess it's possible that the new one was/is defective.

Could it have been due to new replacement the valve needed to seat itself?

Also, wont't the air vent above the expansion ank do the job?

by (mod) - Test the air vent for a stuck float valve

Not exactly; a new air vent shouldn't leak from the get-go unless the leak is due to inadequate seal at the threaded base of the vent where it screws into the air scoop or pipe fitting.

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.

Dry everything off so that you can see exactly where boiler water is leaking out.

See details about dealing with a leaky boiler air vent

at AIR BLEED VALVE LEAK REPAIR  and also check for EXPANSION TANK AIR VALVE LEAKS 

If you need to replace an air bleeder valve

see AIR BLEED VALVE SOURCES - Daniel Friedman

Expansion Tank Odor FAQs

Odors from Heating System Expansion Tank?

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 2017-03-30 by Bill -

Reply by (mod) -

It's common for water leaking out of a hot water heating system boiler, pipes, radiator, or at the expansion tank to smell pretty bad; the same water normally stays in that system for years at a time.

And depending on what chemicals were added to the boiler for freeze protection, that might impact the odor. But the odor is less important than finding and fixing the leak at the boiler or its expansion tank.

No leaks at the boiler means no odors from that source.

About your tankless coil check, be sure to

read TANKLESS COIL INTERNAL LEAKS INTO the BOILER 

You should also review our diagnosis and repair advice

at HVAC SYSTEM ODORS 

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

See WATER ODOR DIAGNOSIS - SULPHUR  for details

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 2017-03-28 by Bill - I

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.

See our article on TANKLESS COIL INTERNAL LEAKS INTO the BOILER 

Thanks for asking, Bill.

by Bill - maybe iron bacteria causing boiler smells

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

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.

by (mod) - you shouldn't have to keep draining the expansion tank

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.

Expansion Tank Air Charge FAQs

Should there be air in the expansion tank?

Is there supposed to be air in the expansion tank or holding tank on a boiler system On 2017-02-15 by Anonymous

by (mod) - Yes

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.

From the factory, an expansion tank that uses an internal bladder typically is delivered with 12-15 psi of air pre-charge.

Bladderless expansion tanks or "header tanks" have NO factory air pressure pre-charge. Rather, to set up those tanks the tank is drained of all water, allowing air to enter the tank at atmospheric pressure.

Then when you re-open the valve between expansion tank and boiler, the boiler's pressure (about 12 psi when the boiler is cold) will push some water into the expansion tank until its internal pressure equals that of the boiler - about 12 psi.

Also see these EXPANSION TANK PRESSURE FAQs

How much pressure should the expansion tank have?

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 2016-12-22 by John

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.