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Obsolete boiler pressure relief valveRelief ValveRELIEF VALVE LEAKS Leak Diagnostic FAQs
Questions & Answers on the causes/cures of T&P Valve Leaks

  • RELIEF VALVE LEAK FAQs - CONTENTS: Questions & answers about how to diagnose & fix a leaky pressure relief valve or leaky TP valve on a boiler, water heater, or water tank
  • POST a QUESTION or READ FAQs about the causes & cures of leaks and discharges from pressure relief valves or TP valves
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Temperature & pressure relief valve leak FAQs:

Questions & answers about leaks in TP valves: what causes temperature or pressure relief valves to drip or leak and what are the proper and safe repair steps to diagnose and fix the trouble?

This article series describes the causes of leaks, drips, or discharges from pressure relief valves, temperature/pressure relief valves, or TP valves found on heating boilers, water heaters, or the simpler pressure relief valves found on water pressure tanks.

Watch out: a dripping or frequently spilling T&P valve is dangerous because those very leaks can eventually cause the valve to clog and then to fail to open when it should.



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Leaky or Dripping Water Heater Pressure & Temperature Relief Valves

Leaky unsafe relief valve (C) Daniel Friedman[Recently-asked questions & answers about temperature/pressure relief valve leaks, posted originally at RELIEF VALVE LEAKS - home page for this topic.

Question: Field Report - How to Diagnose a TPR valve on tankless gas boiler spills on a regular basis

I have a tankless gas boiler and after maybe 6 years in use, it has started relying on the pressure relief valve on a regular basis, such that it fills a 5 gallon bucket about once a week.

During a heating cycle, the boiler steadily climbs from about 15 psi to 45, at which point the pressure relief valve bleeds off a little water into the bucket. Is this a symptom of something I can fix?

There's no floor drain in the proximity of the boiler, so it's kind of annoying, but otherwise it works fine.

I'm also having a problem with one of my Taco ZVC403 Zone Controller zones that stays on just a few seconds - discussed separately at ZONE CONTROLLER TACO ZVC403 ]- Karl Peterson by private email 2017/12/09

This discussion is indexed as RELIEF VALVE LEAK DUE TO EXPANSION TANK

Reply:

By tankless gas boiler, is that boiler used for heating your home or is it supplying domestic hot water?

Guessing it's for heating your home, a frequent spillage at the temperature/pressure relief valve is unsafe, although we are of course glad that the valve is doing its job.

Tell me the brand and model of your heater and we can look for its manual to see what the manufacturer says about proper operating temperature,

If your relief valve is original equipment chosen by the manufacturer and is designed to open at 45 not 30 psi, then your system is designed to operate at a bit higher pressure.

The usual underlying causes of a temperature/pressure relief valve to open (high temp or high pressure or both) are at RELIEF VALVE LEAKS

Zilmet expansion vessel Type 541/L leak diagnosis (C) InspectApedia.comIf you haven't seen that article, its diagnostics are a good place to start.

Closed hot water heating systems can also leak due to thermal expansion.

Reader follow-up: water pressure controls on my Cosmogas Boiler vs Relief Valve Leaks

[The Cosmogas boiler manual for this heater/water heater gas fired combo boiler as well as company contact information is at COSMOGAS® boiler / water heater combo manuals - thanks to Karl for providing this document - Ed.]

Below is a photo of the front panel. It is supposed to have a minimum of 12 psi, and a max of 30psi according to the manual, but the relief valve is at 50psi (another photo below.)

Cosmogas BMS 15/29 Boiler control (C) InspectAPedia.com Karl Peterson

At rest, the pressure is indeed about 12-15 psi generally, but after 2 or three cycles of the heater heating up water for the radiant heat, the pressure climbs to about 45psi, and the valve starts to bleed off pressure.

Its done this all last heating season, and possibly the previous season as well. it never does this in the summer time (or when the heat is off) and as I mentioned previously, it didn't do this at all for the first 6 or 7 years it was installed. There is no banging or hammer noises.

50 psi TP Relief valve (C) InspectApedia.com KP

[Click to enlarge any image] Above: Zurn Model P1000A temperature/pressure relief valve rated for 200,000 input BTUH and opening at 50 psi.

This TPR is rated to handle thermal expansion of hot water and complies with ANSI Z21.22 / CSA 4.4 relief valve specifications.

Cosmogas® Boiler Relief Valve Leak Diagnosis & Warnings

Zurn 50 psi TPR valve data tag (C) InspectApedia.com Karl Peterson

Watch out: I note on p. 13 that the Cosmogas boiler manual for your heater specifies a 30 psi TPR valve.

I had some trouble making out the details in your photo but it looks to me as if you've got a 50 psi TPR valve installed. That might indicate someone was already having pressure problems with this system, or it might be that the higher psi is appropriate for a radiant floor system.

In any event one should never substitute a higher-pressure-rated TPR valve than specified by the manufacturer without their explicit approval. (A too-high pressure could cause the boiler to explode, causing a BLEVE - BLEVE EXPLOSIONS discusses this.

Watch out: The manufacturer also warns about TPR discharge due to thermal expansion HOT WATER PRESSURE EXPANSION RATE discusses that issue.

That's why your system would probably have a hot water thermal expansion tank installed (HOT WATER EXPANSION TANKS ) , and as we said earlier a failure of that tank (such as a rupture of an internal bladder) could then cause TPR valve leaks.

There should be a water pressure feeder/reducer for your boiler keeping the cold pressure to 12 psi - maybe a bit higher if yours is a tall home. That will prevent your booster pump or your supply water pressure from overpressurizing the boiler.

See COSMOGAS® BOILER MANUAL Models BMS & BTS [PDF] (2002)

Watch out: A tankless coil type hot water supply can also drive up system water pressure if the coil develops a leak. The coil leaks water at house system water pressure into the heating boiler's own water system. Normally the house water supply will be above 30 psi while starting cold water pressure in a boiler is at 12 psi. TANKLESS COIL INTERNAL LEAKS INTO the BOILER

Watch out: another possible cause of leaks at your boiler's TPR valve is one we mentioned earlier, water hammer - discussed beginning at WATER HAMMER NOISE DIAGNOSE & CURE

Reader follow-up:

Yes I noticed that as I was rereading the manual the other day (about the 30psi TPR valve) and yes, the one installed currently is a 50psi model. I can't remember if that was changed or not, but I don't believe so. In any case, if it were a 30psi model, this problem of the water being released would be that much worse.

I understand that water coming out of the valve is preferable to an explosion, but I only say this to indicate that there is clearly an issue here. I had this system put in, so, there is no history that I shouldn't know about (if I can remember it)

Anyway, the line about domestic water pressure is something that changed a few years ago. Yes, this unit provides both hot water for the floors and for domestic use. We recently had an extra pump installed to provide greater water pressure to the building, as the top floors were suffering from reduced pressure from an RPZ(?) that we had to have installed. (We're a 4 floor building, one unit to each floor, and each floor has its own heating and hot water equipment.)

I will look again at the boiler tonight to see if I can find any evidence of a coil leak inside the boiler.

There is a small expansion tank inside the boiler - I will look that over tonight as well.

Reply:

There should be a water pressure feeder/reducer for your boiler keeping the cold pressure to 12 psi - maybe a bit higher if yours is a tall home. That will prevent your booster pump or your supply water pressure from overpressurizing the boiler.

As you describe each floor having its own heating boiler for both heat and hot water, 12 psi would be the normal input water feed pressure when the boiler is cold. When the boiler is at full operating temperature, typically somewhere under 200°F the system pressure should be under 30 psi.

You won't "see" a cold water supply leak into the boiler through a corroded coil since that's hidden inside the boiler.

But you can spot it by noticing the boiler pressure going up when the feed to the boiler is closed completely.

This analysis is made more difficult by the fact that pressure goes up when the boiler heats up as well. TANKLESS COIL INTERNAL LEAKS INTO the BOILER is intended to help sort that out.

Reader follow-up:

Attached is the manual for my boiler - I have the BMS 15/29. I can find no information about regulating pressures inside the boiler.

The COSMOGAS® BOILER MANUAL Models BMS & BTS [PDF] (2002) for this heater/water heater gas fired combo boiler as well as company contact information is also found at at COSMOGAS® boiler / water heater combo manuals.

Reply:

Something might be mistaken here but I note on p. 13 that the company specifies a 30 psi TPR valve. I had some trouble making out the details in your photo but it looks to me as if you've got a 50 psi TPR valve installed. That might indicate someone was already having pressure problems with this system, or it might be that the higher psi is appropriate for a radiant floor system.

In any event one should never substitute a higher-pressure-rated TPR valve than specified by the manufacturer without their explicit approval. (A too-high pressure could cause the boiler to explode, causing a BLEVE - BLEVE EXPLOSIONS discusses this.

The manufacturer also warns about TPR discharge due to thermal expansion HOT WATER PRESSURE EXPANSION RATE discusses that issue. That's why your system would probably have a hot water thermal expansion tank installed (HOT WATER EXPANSION TANKS ) , and as we said earlier a failure of that tank (such as a rupture of an internal bladder) could then cause TPR valve leaks.

[Besides a failed hot water thermal expansion tank,] a tankless coil type hot water supply can also drive up system water pressure if the coil develops a leak. The coil leaks water at house system water pressure into the heating boiler's own water system.

Normally the house water supply will be above 30 psi while starting cold water pressure in a boiler is at 12 psi. TANKLESS COIL INTERNAL LEAKS INTO the BOILER

Reader follow-up - check for abnormal boiler water feed pressure, check for tankless coil leaks

Yes I noticed that as I was rereading the manual the other day (about the 30psi TPR valve) and yes, the one installed currently is a 50psi model. I can't remember if that was changed or not, but I don't believe so. In any case, if it were a 30psi model, this problem of the water being released would be that much worse.

I understand that water coming out of the valve is preferable to an explosion, but I only say this to indicate that there is clearly an issue here. I had this system put in, so, there is no history that I shouldn't know about (if I can remember it...)

Anyway, the line about domestic water pressure is something that changed a few years ago. Yes, this unit provides both hot water for the floors and for domestic use. We recently had an extra pump installed to provide greater water pressure to the building, as the top floors were suffering from reduced pressure from an RPZ(?) that we had to have installed.

(We're a 4 floor building, one unit to each floor, and each floor has its own heating and hot water equipment.)

I will look again at the boiler tonight to see if I can find any evidence of a coil leak inside the boiler.

There is a small expansion tank inside the boiler - I will look that over tonight as well.

Reply: homing in on a problem with the boiler's expansion tank

Yes you want the TPR to spill.
Yes more will spill at 30 psi.
But you don't want to over-pressurisze the system.

There should be a water pressure feeder/reducer for your boiler keeping the cold pressure to 12 psi - maybe a bit higher if yours is a tall home. That will prevent your booster pump or your supply water pressure from overpressurizing the boiler.

You won't "see" a cold water supply leak into the boiler through a corroded coil since that's hidden inside the boiler.

But you can spot it by noticing the boiler pressure going up when the feed to the boiler is closed completely. The study is made more difficult by the fact that pressure goes up when the boiler heats up as well. TANKLESS COIL INTERNAL LEAKS INTO the BOILER is intended to help sort that out.

also,

As you describe each floor having its own heating boiler for both heat and hot water, 12 psi would be the normal input water feed pressure when the boiler is cold. When the boiler is at full operating temperature, typically somewhere under 200°F the system pressure should be under 30 psi.

Reader Follow-up: cold system pressure is in normal range & boiler temperature limit is well below 200F, no water hammer

Yes, when the system is cold, the pressure is at about 12-15 psi according to the meter on the front of the boiler, and there is a pressure reducing valve on the line into the boiler. The boiler is set to 150 degrees.

There are no hammering noises with this boiler.

Reply:

I think this is in my article on leaky coils but I want to suggest: if you can stand having no hot water for a time you can try turning off the cold water supply into the coil, dropping the boiler pressure down to normal, then leaving the cold off (to the coil) to see if the boiler pressure creeps back up or not.

(Presuming we're confident that the stop valve really closes fully - you can test that by seeing that hot water pressure at the tap falls to zero). Or you can do that when leaving home for a time or when nobody needs hot water.

Reader Followup: check pressure on the heating loop side ?

we do this to limit the heaters function to heating water to the radiant heat flooring?

Reply: no, check the domestic hot water system - tankless coil

We're closing water into the domestic hot water heating coil - shutting off the hot water for your shower.
The radiant heat part of the system will continue to work.
By closing off water into the tankless coil (stopping hot water flow in the home) and seeing that pressure doesn't rise (you dropped boiler pressure down to normal at the start of this test by draining off a bit of water from the boiler drain), we will confirm that the problem is a leaky coil.

Remember water inside the coil enters cold, gets heated by the physically separate boiler water, and flows out hot onwards to your plumbing fixtures. Details of how this works are at TANKLESS COILS

If boiler pressure continues to rise when the coil is (for sure) isolated from the system then we will suspect a bad water feeder / pressure-reducer valve feeding more water into the boiler itself.

Reader Followup:

Anyway, here's a video of the situation. VIDEO of COSMOGAS BOILER OPERATION [85MB .mov file]

https://drive.google.com/open?id=1fbzRJV7SIGBV7xqZ2wAijHMdQ_X4CRfa

Shutting off the cold water in doesn't seem to change anything.

Looking inside the boiler, I can see some corrosion around the bottom of the red expansion tank. I can also see that the expansion tank is only connected to the radiant heat side of the boiler.

Also, there doesn't seem to be another shut off for the cold water closer to the boiler - the one I show in the movie is the closest one.

Reply:

Watch out: your movie shows the heating system going up to nearly 45 psi, well over the 30 psi maximum pressure specified by the Cosmogas boiler manufacturer and to a level at which it would be normal for the TPR valve to open and spill to relieve pressure. This is an unsafe heating system, particularly should the TPR valve become clogged by repeated passage of heating system water (and mineral deposits.)

Right, the expansion tank only needs to be connected such that it responds to pressure in the closed-system boiler and piping. IT has nothing to do with the tankless coil making domestic hot water.

But if the coil leaks into the boiler then that pressure increase will be continuous up to the point at which boiler pressure is about the same as house water system pressure. That will overwhelm an expansion tank even if the tank is otherwise in fine shape.

There is bound to be a shutoff somewhere on the cold water entering the hot water producing coil. Follow the piping back from the boiler's connection of cold water to coil - this is separate from the cold supply that feeds the boiler itself.

To look for a tankless coil leak into the boiler, shutting off the cold water into the coil will not immediately show a result.

To watch for the effects of a leaky tankless coil overpresssurising the boiler you will need to

- turn off cold into the tankless coil (not into the boiler itself)

- drop the boiler pressure to 12 psi when the boiler is cold

- wait and watch - since the rate at which boiler pressure would be pushed up from a coil leak depends on the size of the coil leak and on the pressure difference across the leak (house water system pressure and boiler pressure)

- turn the cold water supply to the coil back on and again watch for a pressure increase on the boiler side

Really? Keep in mind that if the expansion tank has failed the system pressure will increase when the boiler heats up and the relief valve may spill when the tankless coil is out of the picture.

We need to investigate that thermal expansion tank on your heating system.

Zilmet Type 541/L Expansion Vessel (C) InspectApedia.com Karl PetersonReader follow-up - investigating the expansion tank

I'm looking more closely at the expansion tank - it is a Zilmet 10L tank, and according to this page, it should have an internal bladder. (there's no information about the type of tank it is in the manual) I thought I'd check the pressure via the bicycle style air valve, but a bunch of water came out instead - perhaps the internal bladder has been punctured, and it's completely full of water?

[Click to enlarge any image] Photos: Zilmet Type 541/L OEM type expansion tank or expansion vessel (in the U.K.) and below, its data tag.

I also found some installation manuals for the complete line of Zilmet expansion tanks(although mine isn't listed), which says their tanks have a life span of about 5 years, and mine is closing on 10.

Reply: Evidence of Bladder Failure in a Zilmet OEM Type 541/L flat heating boiler expansion tank

If you can get me a photo of your actual tank as well as its label I'd like to research it.

If the tank uses an internal bladder and if water came out of the air (adjustment) valve then the bladder has burst and you've diagnosed what's probably the trouble with the TPR valve leaking.

Still there may be a second problem and a source of abnormal system pressures - IF you see that when cold your boiler pressure is abnormally high - say over 12-14 psi or if when the system is hot the pressure is at or over 30 psi.

Zilmet Type 541/L Expansion Tank data tag (C) InspectApedia.com Karl PetersonWatch out: Having confirmed that the tank uses an internal (butyl) bladder to keep water and air separated, that it uses an air valve to check tank pressure, and that you had water squirting out of your tank's air valve it's a reasonable conclusion that the tank's bladder has failed. You will want to replace this tank.

The OEM description I found was from a UK vendor but they're sold also in the US. I found listings by searching for "Zilmet Type 541/L pressure tank"

I would fix this first, but you should also continue to investigate whether or not there are other defects causing abnormally high water pressure in your system by making simple observations of the system's pressure as I described.

Paraphrasing from the company's information and other sources:

This Zilmet Type 541/L (made in 2006, 5-year warranty) "flat" expansion tank tank has a maximum working pressure of 3 bar (about 43 psi) so if it has been exposed to higher pressures that could have contributed to a failure.

This Zilmet product is specifically made as an OEM used by heater manufacturers. I'll include the manual for your tank [PDF attached] and an image of the currently-sold version of your OEM tank

Zilmet expansion vessel Type 541/L leak diagnosis (C) InspectApedia.comTanks in this shape are selected for space-saving, perhaps here to fit into the boiler chassis for a wall-hung condensing boiler.

The Zilmet expansion tank models for which I reviewed information all use a butyl or synthetic SBR rubber internal bladder or membrane (replaceable in some models).

Your Zilmet 541/L is a 10L (or perhaps 12L) model is rated for a maximum pressure of 3 bar (14.5 psi) maximum pressure and comes with a1-bar factory air pre-charge.

Some Zilmet expansion vessel models handle up to 150psi and 210F, and have a factory air pre-charge of 40 psi but your tank is a different model not described exactly in that literature. One can find some literature about the Zilmet 541/L from UK vendors.

Watch out: notice that the factory air pre-charge is 1 bar - or 14.5 psi. So on your system the tank will start accepting water (from the closed hydronic system) when that system pressure exceeds 14.5 psi and will work correctly up to about 45 psi. which is above where the TPR valve should dump.


On 2017-03-15 by (mod) - relief valve leaks after draining expansion tank and installing new valve

Pressure release valve leaks can be caused by several things, as we cite at RELIEF VALVE LEAKS

Once you're sure that there is a normal air charge in the heating system expansion tank,

then I'd start by checking that the cold boiler pressure is normal - usually around 12 psi and that pressure doesn't creep up even when the boiler is off.

Then I'd look for a water hammer problem.

On 2017-03-15 22:46:09.212307 by Rick

Pressure release valve popped. Water everywhere since I was at work. I replaced the valve and drained all the water from the expansion tank, no bladder.

When I try to refill the system the pressure goes above 26 or so and the valve blows. It will not let me refill the system with water. Any ideas. Thanks

On 2017-03-15 16:00:21.189409 by (mod)

Trevor:

If the TP valve is leaking and system pressure is well below the pressure at which the valve should be leaking, AND if the pressure reading is accurate (you can test that by making an independent measurement of boiler pressure)

then the valve is probably defective and needs replacement.

A more subtle cause of TP valve leaks that will be intermittent is a water-hammer problem anywhere in the plumbing or heating system.

The article RELIEF VALVE LEAKS lists the likely causes of a leaky TP valve. Please take a look at those and let me know what you find or what questions remain.

On 2017-03-15 by Trevor Humphreys

Release valve leaking. Pressure is 20. Can't figure out what is wrong

On 2016-10-10 by (mod) system pressure goes up to 80 and the relief valve still leaks

Bonnie

I'm unclear about what equipment you're working on, where you reduced pressure, and other key matters.

If you are talking about leaks at a heating boiler that uses a tankless coil, house water could be leaking into the boiler through the coil; or an automatic water feed valve at the boiler may be defective; or a house main pressure regulator may be bad. that's enough shotgunning with so little info.

Watch out: the situation you describe is unsafe and risks a boiler explosion or BLEVE

On 2016-10-09 by Bonnie

Replaced the pressure release valve and lowered the water pressure to 50 sometimes it still goes up to 80 and the release valve still leaks what do i need to do

On 2016-05-30 by (mod)

A drippy TP valve risks a BLEVE explosion as one day the mineral build up from water passing through the valve may simply clog it up. So replacing it is smart.

CHeck for a failed diaphragm in the water feeder/pressure reducer

Check for a failed expansion tank

On 2016-05-18 by Eddie

This all started when I installed a mixing valve on the domestic coil size as it didn't have one. They were getting boiler water in the shower, sink, etc. Anyways, when I turned the system back on. Thats when the issue arose. The valve drips all the time

. When the boilers at 15 psi or 0. I installed a new TPR valve and it stopped. But when I opened it to test the new valve, the dripping started again. The gauge works. The fill valve may be faulty from I saw today while trouble shooting. And the expansion tank is the bladder style. I'll also add that the expansion tank spit a bit water when I pressed on its "pin".

I'm going back tomorrow to check the expansion tanks psi and replace it if need be. My friend is really pushing to not change the fill valve as his "boiler guy" told him he didn't have too. Sorry for the long winded story. Just seems to be a new issue every day and I'm trying to get the best advice possible. Thank you

On 2016-05-17 by (mod) - pressure gauge at zero and temperature at 180 deg means one of those indicators is not working

Eddie

If the pressure gauge says zero and the temperature at 180 something is not working. If there is water in the boiler and the gauge is working properly the TPR ougnt not be leaking at 180F unless the water feeder valve or pressure regulator are overpressurizing the boielr. Start by replacing the gauge and the TPR valve.

Watch out: if you're not trained and make a mistake the risk is blowing up the home or burning it down.

On 2016-05-16 by Eddie

I'm working on my friends boiler. The pressure relief valve is leaking. Yet the pressure on the gauge said 0. Temperature is still at 180 so I assume the expansion tank is still good? Maybe just a bad relief valve?

On 2016-04-11 by (mod) - blocked radiator valves

Anon:
Perhaps debris from disturbed plumbing connections has blocked the entry passage in two of your radiator valves.

On 2016-04-11 by Anonymous

I've just had all the valves changed on every radiator in the house, unfortunately there are two radiators that will not heat up! I've tried bleeding them I've tried balancing the system, could the problem be at the valve near the boiler?

On 2016-01-21 by (mod) - If the boiler pressure is over 30 psi the TP valve SHOULD be dumping

If the boiler pressure is over 30 psi the TP valve SHOULD be dumping to avoid a potentially fatal BLEVE explosion of your boiler. Your system needs service: the problem can be at a pressure reducing valve, water feed valve, leaky tankless coil, or something else.

On 2016-01-21 by Anonymous

I don't have no less and the presure in the gage said 40 psi what's the problem

On 2015-12-19 by (mod)

Review the common TP valve leak causes above; I'd be very interested if your boiler's TP valve leaks was not one of those. Sometimes a TP valve leak cause is not so obvious, such as water hammer, surges in boiler temperature due to an aquastat problem, surges in boiler pressure due to a problem in the water pressure regulator or feeder, or even a leak in the tankless coil on a boiler.

On 2015-12-18 by Lisa

just to follow up: the TP valve seems to be fine, there has been no sign of further leaks. The boiler pressure was also very low so for now it looks like the problem is resolved. I still find it troubling that these parts on the storage tank failed within days of the boiler installation, but I don't think I'll ever really be able to get to the bottom of it.

thank you so much for your advice!

On 2015-12-14 20:55:32.033481 by Lisa

yes I know - these parts failed last week, so the pump was replaced last thursday, and the PT valve was replaced on friday. I'm waiting to hear from the tenants if there is any evidence that the valve is leaking again, if there are any other leaks, and what the pressure gauge says.

Based on that info (and your advice so far) I will move forward. Believe me, I'm not taking any chances with this.

On 2015-12-14 19:18:59.610014 by (mod)

Lisa

A leaking temperature/pressure relief valve is UNSAFE. Over time water leaking through the valve body can leave mineral deposits that clog the valve, ultimately meaning it may not properly respond to an unsafe condition such as boiler over pressure or over temperature. IN turn that can cause a dangerous BLEVE explosion.

So if the valve is still leaking at your system you want to have a heating service tech out to the property promptly. Don't panic, but don't be unsafe either.

On 2015-12-14 19:09:20.164837 by Lisa

this is so helpful - thank you! and yes I will report back. Unfortunately I'm not living in the house so I have to wait for my tenants to get back to me about the pressure reading, then I'll proceed from there.

On 2015-12-14 18:38:39.677104 by (mod)

If the expansion tank is found to be NOT defective (not waterlogged or for newer tanks, NOT to have a burst bladder) then yes one would next check the system pressure regulator / water feeder.

Basically IF you see boiler water pressure over 30 PSI when the boiler is hot, the pressure is too high. Most systems also show about 12 psi - certainly under 20 psi - for residential homes when the system is cold.

Call your heating service company. LEt me know what you're told.

On 2015-12-14 18:27:32.184469 by Anonymous

Hi danjoefriedman

I appreciate the quick response. The thing that concerns me is that they didn't do any work on the pump or the relief valve! These were installed several years ago, had no problems, the plumbers said it was ok to keep that part of the system in place so as far as i know they didn't touch it. The fact that both of these parts started leaking within days of replacing the boiler makes me worry there is a more serious problem. Like too much pressure in the system ;)

On 2015-12-14 17:53:37.920395 by (mod)

Lisa

I can't tell the cause of the leaks you describe from just an e-text, but certainly it is true that a bad expansion tank can cause relief valves to release hot water. That's not at all the same as a leak at a piping connection. Water coming out of the relief valve discharge tube is in response to an overpressure condition in the system.

Leaks where the valve screws into the boiler are a plumbing problem.

Leaks at a circulator would more likely be a bad gasket, connection or mounting problem.

On 2015-12-14 17:15:30.857794 by Lisa

I had a new oil fired, tankless, steam boiler installed and the existing hot water storage tank was re-used/left in place.

In less than one week the circulator pump sprung a leak (it was actually spraying all over the place) and once that was fixed, the TP valve sprung a leak the same day.

The plumber says these leaks "merely" happened because the storage tank was not replaced along with the boiler, but I think this sounds very fishy - it sounds like way too much of a freak coincidence that both of these components would fail back to back, within days of replacing the boiler.

The storage tank and pump were 7 or 8 years old at the time of the boiler replacement, and as far as I know the TP valve was also replaced with the tank and pump, but I am not 100% certain of that.

Any ideas what the root cause of the pump and TP valve leaks could be?

many thanks!!!

On 2015-10-24 21:56:28.802886 by dave

Hi I have a problem my with expansion tank I cant get air into it with pump or compressor, removed air valve
and the water did not come out used a small rod to push on it and its blocked.

On 2015-08-07 17:57:46.284641 by (mod)

Thanks for your comment, John. We agree that it is crazy, and very dangerous, to make try a "DIY" repair to a TP valve on heating equipment.

Watch out: most of us who've worked in the field have seen some pretty crazy and scary modifications ranging from plugs and valves to "fix" a leaky relief valve (DO NOT DO THAT or YOU MAY KILL EVERYONE NEARBY) to use of drips from the TPR valve to water the cat bowl.

On 2015-08-07 16:04:28.889741 by John Tedesco

Steam pop safety valves have a tamper proof seal attached to detect whether the valve has been tampered with.

As per the ASME CODE, only the manufacturer of the valve may repair or re-adjust the safety valve. In almost every case the safety valve that leaks is already damaged.

Continuing to operate a boiler with a leaking safety valve may result in a boiler explosion.

Question: replaced defective pressure relief valve - not tight enough?

(Apr 21, 2014) Jeff said:

I put in a new water heater and when it came the pressure relief valve was bent and defective,the place I bought it gave new pressure relief valve I put it in but did not tighten it as far as it could go in because than I would have a problem of putting the line into pressure relief valve.

I can turn it by hand but with line in you can not turn it.It does not leak and valve works.will this be a problem down the road?

Reply:

Jeff, I am nervous about promising the safety of such a critical device in a DIY installation that I cannot see.

If the valve is easily rotated by someone bumping the TP valve extension tube it's too loose. Or, as up surmise, it's too loose if it leaks.

But I understand very well the problem of where you end up when rotating the TP valve into place on a heating appliance, as we for sure want the valve body facing down.

You have two options:

1. check the valve several times over the next week with the heating system at full operating temperature and pressure - looking for leaks and check again at periodic service or if you see mineral salts build-up around the valve or water on the floor or boiler side.

2. remove the valve and us additional turns of teflon tape so that the valve is adequately snug while pointing down properly.

Question: how to diagnose dripping from the pressure relief valve

(June 1, 2014) Frank 06/01/2014 said:

I have a 31-yeay oil boiler (tankless water heater), which had small water dripping from the pressure relief.

The pressure and temperature was 20 psi and 180 degree. The boiler does not ignite frequently now because of the beginning of summer season. Water dripping from the pressure relief significantly increased when the boiler was tested to heat the house, and the pressure reading went up quickly to 30 psi.

The water released from the pressure relief contained a lot of yellow residue.

Greatly appreciate if you have any thoughts.

Reply:

Diagnose dripping TP valves on a heating boiler

If the TP valve is leaking and the heating boiler temperature is BELOW the 200degF limit I suspect either overpressure in the boiler or a defective valve.

The fact that leaks increase when the boiler is heated up is consistent with either of those conditions.

Pressures close to or over 30 PSI will spill the valve.

If your boiler has a tankless coil the coil could be leaking water into the boiler raising its pressure.

With the boiler OFF and cooled down to room temperature, remove water to drop pressure to 12 psi (or slightly higher if your home is more than 3 floors tall).

Leave the boiler off and watch for a pressure increase - that'd indicate a leak into the boiler or a faulty water feed valve.

Diagnose dripping TPR valves on a water heater

Open a faucet anywhere in the building. If the dripping stops, most likely the cause is thermal expansion of hot water.

Question: Boiler set relief valve off

8/17/14 Donald Fletcher said:

The high low limit device on my Weil Mclain natural gas boiler failed. Temp went well over 200F. This set the boiler relief valve off. I replaced the high/low device and the well the copper sensor end fits in. There was no scale on the old well or the sensor end of the high/low that was replaced. There was just a black film coating, which was easily wiped off.

This new high/low device seems to work but it is not accurate. In order to get the boiler to shut off at 180F the setting on the high/low must be set to 160F.

In Aug 2013 TP valve activation was a real problem which led to new TP, Expan tank, auto water feeder valve, back flow valve and as mentioned at RELIEF VALVE LEAKS the last item the high/low limit replaced Oct 2013.

All was from OCT 2013 till Aug 13 2014 and then the TP was activated for reasons unknown other than the pressure gauge read 30lbs which is the trigger point for the TP. Expan tank checked out at 12 PSI. I do have a street fill valve and this valve was closed since OCT 2013 and boiler pressure was checked every month or so and was a constant 14/17 PSI.

There is a Bock indirect water heater that I thought could have a coil pin hole that opens when it has a mind to, allowing potable street water into the boiler through the coil. System is up a running now for the last several days and the pressure is at a steady 17psi. Hot or cold the pressure is always the same 17psi. I have verified the pressure with a separate 0-30psi gauge.

So do you have any thoughts on the matter that can I apply. Thanks

Boch indirect and boiler 19 yrs old

Reply:

For temperature sensing errors on typical modern aquastats and limit switches:

Do you think the problem could relate to poor thermal contact between the Aquastat's sensor probe and the surface of the well into which it is inserted?

Did you use the manufacturer's recommended thermal conductive grease? (Some heating techs don't)

Thermal grease is recommended by limit switch manufactures for units whose sensor probe fits into an immersion well in a heating boiler or water heater. Absence of good contact between the sensor tip and the sensor well sides can explain off-spec temperature sensing as well as (I think) odd burner on-off cycling.

Reader follow-up;

Dan, I was not aware of the thermal grease. Did not see it mentioned in the directions.

It would seem the grease could help get the high limit set at 180F and a actual boiler flame off at 180F. However it is worth noting that the boiler does flame back on at 140F. I would gladly pull the probe and use thermal grease in an attempt set things to right. Well worth trying. :) - Don Fletcher

Reply:

For a limit control sensor to work properly when inserted into the immersion well on a boiler, it must be in contact with the inner surface of the immersion well; the grease assures good thermal contact. The limit controls I've bought and installed generally came with a little tube of the special grease. Some time ago some heating techs avoided using the grease claiming it solidified and made later service difficult. That problem was corrected. In sum , the control should be installed according to the manufacturer's specs. Check with the company who made your unit. Let me know if youre' told something different. The thermal grease was commonly provided with older Honeywell aquastats and is also sold at plumbing and heating suppliers - IF your unit's manufacturer specifies its use (not all do) you'll want to add it.

Reader follow-up

Well, I it's a Honeywell L4080D1226 and I called them today and was told heat conductive compound is not supplied with the limit assembly. There is no mention of the grease in the Weil McLain parts list. So I took the sensor body out of the well and tilted the sensor in an effort to get good metal to metal contact. But, the results changed nothing. I did not call Weil Mclain yet but I will. I will also get some compound to put in there as well. The well is not a snug fit to the sensor, that is to say there is air space. So there is room for thermal compound.

This morning with everyone taking showers I took pressure readings while the boiler was fired up. What was 17psi cold or hot has become 17psi cold & 21psi hot. Higher than needed but OK I think if it stays that way. Pressure release valve is not dripping.

...

Well the boiler is at 100F and I just checked the pressure. It is 21psi. That makes what I said earlier (17psi cold 21psi hot) very wrong.

The street fill valve is closed and as far as I know the indirect water heater is the only other place the extra pressure can be coming from. Although it would seem it is doing so in short intervals.

Reply: other sources of abnormal boiler or water heater tank (cylinder) pressrure

Donald

If your boiler or your hot water system includes a tankless coil or any equivalent (a coil containing house water (to be heated) immersed in the vessel whose TP valve is leaking, shut OFF water entering that coil - to see if house pressure in the coil is sending water through a coil leak into the boiler.

Also see

inspectapedia.com/plumbing/Tankless_Coil_Leaks.php

Reader follow-up:

Coil contains circulated boiler water. Hose water at street pressure may be leaking into the coil by way of a pin hole in the coil. So we are on the same page so to speak.

I have shut of boiler supply to the coil numerous times. But it is not easy to prove out the problem because it happen very intermittently. I will monitor it overnight and see the PSI in the early morning. If it's like past history it will still be 21 lbs come morning.

If I wait it out it could weeks or months before the hole will open up and cause it to happen again. There are no leaks from any pressure relief valves at this time.

The Bock indirect water heater TP has never leaked. Thanks for helping me with Dan, I really appreciate it.

Reply:

Donald

Usually house water pressure is higher than boiler water pressure - but not always.

If the boiler is COLD its internal pressure may be just 12 psi. In that case house water pressure inside the indirect water heater tank, sitting at say 30 psi to 60 psi, might indeed leak INTO the coil through which boiler water is circulating.

You should see that as a pressure increase on the boiler pressure gauge as long as you've left the system off long enough to have a boiler-cold-before and boiler-cold-after pressure reading.

The case you describe, house water pressure leaking INTO the heating coil inside of an indirect-fired water heater is similar to the tankless coil leak case I describe in the article linked below.

Keep us posted.

Question: the pressure relief pipe is dripping constantly

(July 21, 2014) Ian said:

I have a two year old closed vented system. The meters show just over 1 bar pressure which I top up every 6 months. I have noticed the pressure relief pipe is dripping constantly, but can find nothing to indicate why this would be happening.

It is a very slow but constant leak, but the positioning of it is causing some brickwork to become slowly saturated and damp smell inside the house.

Reply:

Ian we discuss this problem in FAQs and article RELIEF VALVE LEAKS on this topic - look for

- a bad pressure reducer valve or water feed valve

- a tankless coil leaking into the heating system boiler

- a defective relief valve

-abnormal operating temperatures

Watch out this is an unsafe condition. The cause of the dripping TP valve needs to be found and fixed and the valve should probably be replaced too.

Comment: Like a ticking time bomb I don't know when it will happen.

(Aug 18, 2014) Anonymous said:

House pressure here is well above 50psi. Boiler is now at 100F and pressure is 21psi. It would seem that if a pin hole is present it is debris blocked and that is why the pressure is holding steady.

I suspect when the debris is dislodged the pressure then builds in the boiler. Like a ticking time bomb I don't know when it will happen.

Question: boiler pressure keeps climbing

(Aug 19, 2014) Donald Fletcher said:

So the boiler was left cold overnight and the pressure was set at 12 PSI. 4 hours latter it was at 16 psi. Pressure was dropped back to 12 and about 4 hours latter it was 17. I dropped the pressure again and when I awoke at 11 AM it was at 18 psi.

So I dropped the pressure again to 12 and FIRED the boiler up. When I came back 30 minutes latter the boiler was at 17 psi. For grins I closed off all the heating zones at the returns using 2 ball valves. I left it this way for just a couple of minutes.

As soon as I opened the ball valves the pressure dropped from 17 psi to 4 psi. (yes 4 psi).

Reply:

Donald

Of course when the boiler is heated the pressure will increase.

When you left the boiler off did you shut off its water feed valve supply? If so, and pressure increased, either the valve didn't close fully (and the water feeder was overfeeding) or there is a leak into the boiler.

Opened what ball valve? The boiler water feeder? (you could also have a failed water feed valve)

Watch out: a tankless coil leak on a boiler will feed water into the boiler at house pressures and will cause over-pressure and unsafe conditions risking a BLEVE explosion.

(Aug 19, 2014) Donald Fletcher said:

YES, the water feed valve supply ball valve was closed (I call it a street fill valve). After that there is a BFP and after that there is a pressure reducer auto feeder. If the water is coming from the water feed valve supply it would mean the auto feeder is bad as well as it should not allow more water in. It's a 14 PSI auto fill valve.

After I fired the boiler up, 30 minutes pressure was at 17 psi. I closed the off the heating zones by closing the ball valves of the return side off the zones. When I opened those return side ball valves a few minutes latter the pressure fell to 4 psi. So I have no idea whats up with that. I have not been able to duplicate that pressure drop.

I will change the water feed supply valve and close it and repeat test tonight. If pressure still rises I will install new indirect water heater. I am still not confident the water heater is the problem though.

Reply:

Just being complete.

I suspect a coil leak into the system.

(Aug 19, 2014) Donald Fletcher said:
Thanks again for your help. :)

Question:

(Aug 22, 2014) Donald F said:
Here's where I am with this. I replaced the street fill valve as a matter of course since the handle was broken and I wanted to eliminate any issues. The boiler sat overnight off and in the morning it was 100F. I took enough pressure off so I could check expansion tank again, which proved out at 13PSI. I let the pressure reducer auto feeder valve fill the boiler back up. My 0-30 lb pressure gauge read 12psi. I left it like that, with the boiler off thinking I would see a pressure rise in a few hours. When I returned 2 hours later the pressure was 0 psi.

I opened the street water feed supply and again the pressure reducer auto feeder brought the pressure back up to 12 psi. 2 hours later it was 4psi. I filled the boiler again (12psi) and fired the boiler up. When hot, I turned all heating zones on, and I bled them but there was no air.

The boiler never returns to 12psi when cold. When cold its more like 17psi and when hot it's 18.5 psi. To my mind when cold it should go back to 12psi or at least very close to it. If the indirect water heater coil has a pinhole then my 60psi streetwater should have drove the boiler pressure past 30psi and tripped the 30psi pressure relief valve.

So for Wed night & all day yesterday and today the pressure has been the 17-18.5 psi I mentioned earlier.

Reply:

Donald

If the boiler "sat overnight" in an OFF condition I'd be quite surprised for it to be at 100F unless your home is over a thermal spring or something. Overnight with heat off I'd expect the boiler to be at room temperature (say 60 to 65 degF) and the boiler pressure to be down around 12 psi (for a 1 or small 2 story house).

I don't quite understand the combination of 100 degF and 12 psi. Perhaps these gauges are off, stuck, debris clogged, broken.

Then you left the boiler turned off and pressure dropped to zero - that sounds like a leak.

It's possible for boiler water to leak out if its pressure is above street pressure inside a coil, and to experience a leak in when street pressure is above boiler pressure.

Certainly though, if the boiler is shut off and cold it ought not drop to 0 psi.

Are there flow control valves or check valves on this system. Might one or more be sticking?

Question:

Aug 22, 2014) Donald F. said:
Just normally closed heating zone valves at the return side and ball valves on the supply side. These ball valves are left open year round. A BFP and the pressure reducer auto fill valve. Both the BFP and the auto fill are out of the equation because 1st in line street fill ball valve is closed.

It did not lose pressure overnight. It was 12 psi when I went down there. I lowered the pressure to 0 to check expan tank, which was at 13 psi. I then represurized the boiler to 12 psi and 2 hours latter it was 0.

Tonight however the boiler gauge on the boiler to sustem side is reading 24psi and my master 0-30psi gauge is reading 21 so if this continues I will actually be happy because it will give more credence to coil pin hole theary. I call water company today and they said water pressure at their last street test 8" main was 71psi.I will continue to monitor boiler several times per day. I should have a better handle on it by Sat night.

Reply:

Donald,

If you stabilized the boiler at a known pressure, left it off, and made sure that no water at street pressure could flow into the indirect water tank from either its inlet or outlet piping (excluding thus backfill by gravity from above) or even more thoroughly, drained pressure off of the hot water tank,

then if there were a pinhole or larger leak into the heat exchanging coil inside the indirect fired water tank, boiler water should leak out into the water tank (contaminating it) or at best no water would flow.

Question: frequent T&P Valve "reliefs"

(Nov 28, 2014) Anonymous said:
after installing 100 ft of 3/4" Pex sub floor heating , replacing 24 ft of 3/4' copper base board.

I am experiencing frequent T&P valve reliefs. I have replace the the auto feed and the T&P valve, and purged all the air. Utilty water is high 90 psi. Do need to increase the size of the expansion tank. Or do ypu suspect a different problem?

Reply:

Anon

At 90 PSI incoming water pressure your heating boiler's pressure-reducer / water feeder valve may need replacement OR you may need to install two of them in series as is often done in high pressure locations.

(Nov 30, 2014) Anonymous said:
Thanks Dan Joe. Your suggestion is something I need do. As it turns out the Expansion Tank bladder had failed, probably due to the 90 psi when refilling the system.

Reply:

Thanks for the feedback anon -that will help other readers. DF

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Or see RELIEF VALVE, WATER HEATER DIAGNOSTIC FAQs

Or see RELIEF VALVES - TP VALVES - topic home where we include additional relief valve information including for hydronic heating and steam heating boilers used for central heating.

Or see THERMAL EXPANSION of HOT WATER

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