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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Recently-asked questions & answers about temperature/pressure relief vavle leaks, posted originally at RELIEF VALVE LEAKS - home page for this topic.
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 aroudn 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 theven 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:
On 2017-03-15 07:24:42.552690 by Trevor HumphreysRelease valve leaking. Pressure is 20. Can't figure out what is wrong
On 2016-10-10 18:54:40.876348 by (mod)Bonnie
On 2016-10-09 04:40:06.526327 by BonnieReplaced 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 22:33:05.048824 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.
On 2016-05-18 01:15:52.154745 by EddieThis 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 11:50:47.948147 by (mod)Eddie
On 2016-05-16 12:43:04.428378 by EddieI'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 20:20:16.447708 by (mod)Anon:
On 2016-04-11 12:56:39.694246 by AnonymousI'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 17:31:35.305872 by (mod)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 13:25:50.454130 by AnonymousI don't have no less and the presure in the gage said 40 psi what's the problem
On 2015-12-19 17:02:08.803872 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 18:06:25.230721 by Lisajust 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.
On 2015-12-14 20:55:32.033481 by Lisayes 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.
On 2015-12-14 19:18:59.610014 by (mod)Lisa
On 2015-12-14 19:09:20.164837 by Lisathis 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.
On 2015-12-14 18:27:32.184469 by AnonymousHi danjoefriedman
On 2015-12-14 17:53:37.920395 by (mod)
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?
On 2015-10-24 21:56:28.802886 by daveHi I have a problem my with expansion tank I cant get air into it with pump or compressor, removed air valve
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.
(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?
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.
(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.
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.
Open a faucet anywhere in the building. If the dripping stops, most likely the cause is thermal expansion of hot water.
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 above 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
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.
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
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.
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
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.
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.
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.
(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.
Ian we discuss this problem in FAQs and article above 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.
(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.
(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).
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.
Just being complete.
I suspect a coil leak into the system.
(Aug 19, 2014) Donald Fletcher said:
Thanks again for your help. :)
(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.
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?
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.
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.
(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?
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.
Thanks for the feedback anon -that will help other readers. DF
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