FAQs on leaks at temperature / pressure relief valves, set #2.

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.

Q&A on Diagnosing Leaky or Dripping Water Heater Pressure & Temperature Relief Valves

These questions & answers about temperature/pressure relief valve leaks were posted originally

at RELIEF VALVE LEAKS - home page for this topic. Be sure to review the diagnosis, repair, and safety advice given there.

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.

On 2018-09-09 by (mod) -

Let's start by checking the building water pressure to see if it's abnormally High. The other thing you might check is for a water hammer problem.

Then check the causes of leaky TP valves given at

RELIEF VALVE LEAKS

On 2018-09-04 by Ian

Hi. I replaced the following. Water heater. Expansion vessel and pressure release valve . Yet water is still dripping from the pressure release valve. What can I do to stop it?

On 2018-08-26 by (mod) -

Ray,

As I think you're asking about a heating oil or fuel oil leak, not a water leak, let's start at

OIL SUPPLY LINE PIPING LEAKS

On 2018-08-26 by Ray of Zimbabwe Africa.

How do I fix a domestic portable oil heater, which is leaking oil and how do I refill it and where do I have to look.

On 2018-02-16 by (mod) -

Vince

You can check the specifications on your temperature/pressure relief valve by reading its data tag. Typically you'll see that the valve will open at 30 psi or at temperatures above 200F. f

So at 188F and 18 PSI the valve should not be opening. Of course the gauges could be off but it'd be unusual for both temperature and pressure gauges to be so far off.

In this case I'd replace the TPR valve. The fact that you had a bucket under it could be a hint that it's been a chronic leaker. Such valves are unsafe.

A simple external visual inspection of the valve is not sufficient.

There are other causes of TPR leaks such as water hammer. If replacing the valve doesn't cure the problem let me know and we'll proceed from there.

On 2018-02-16 by Vince

I have a pressure relief problem on my Burnham boiler. At first, we found a flooded floor and the plumber noticed a leaky air-vent valve.
I replaced that part and all was well for a week.

Today, I went downstairs and noticed water again; caused by the overflow from a bucket I have under the Pressure Relief Valve. So, I looked at the boiler pressure and it reads about 18 PSI, which is fine. However, the boiler temperature was 188 degrees and headed higher. So, I shut off the Emergency switch.

I recently had the boiler serviced, the Relief Valve looks fine, so I am not sure what's causing the temperature build-up and what to do about it? As it is I have to replace one-room of carpeting that initially got wet, I sure don't want to install new carpet and have this reoccur. Please advise...

On 2018-01-04 by (mod) -

John

Let's start by looking through the causes and cures above on this RELIEF VALVE LEAKS page. Let me know what you find.

On 2018-01-03 by John

The pressure relief value keeps dripping

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

On 2017-09-26 by (mod) -

Nick

That's a good diagnostic start. So we have either a temperature that's too high or actual pressure that's too high in the heating system - you've eliminated a waterlogged expansion tank and a defective TPR valve.

Check the boiler pressure: is it at or over 30 psi? If so then the valve should be opening and venting. In that case we need to find the pressure problem source: perhaps a bad pressure regulator on a water feeder to the boiler, or perhaps a leaky tankless coil sending house water at house water pressure into the boiler.

On 2017-09-26 by Nick

I replaced expansion tank and relief valve on my Smith boiler still leaking through relief valve
Help

On 2017-03-16 by (mod) -

Pressure release valve leaks can be caused by several things, as we cite in the article above

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 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 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 above 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

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

...

Continue reading  at RELIEF VALVE LEAKS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• EXPANSION TANK WATERLOGGED, RELIEF VALVE LEAKS
• HOT WATER EXPANSION TANKS
• RELIEF VALVES - TP VALVES - home
  • RELIEF VALVE DISCHARGE TUBE
  • RELIEF VALVE LEAKS
  • RELIEF VALVE LEAK DUE TO EXPANSION TANK
  • RELIEF VALVE, TP VALVE, BOILER
  • RELIEF VALVE, TP VALVE, STEAM BOILER
  • RELIEF VALVE, TP VALVE TEST
  • RELIEF VALVE, WATER HEATER
  • RELIEF VALVE, WATER TANK
  • TUNDISH used in PLUMBING
  • WATER HEATER PRESSURE-ONLY RELIEF VALVES
• THERMAL EXPANSION of HOT WATER
• WATER HEATER LEAK REPAIR

Suggested citation for this web page

RELIEF VALVE LEAK FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to T&P RELIEF VALVES

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