Questions and answers about pressure/relief or temperature/pressure relief valves: TP Valve Installation, Defects, & TPR Valve Inspection.

This article series explains how to install, inspect, troubleshoot, repair pressure / temperature relief valves or straight pressure relief valves used on heating boilers, steam boilers, water heaters, and even on water pressure tanks. This article explains what TP or pressure relief safety valves are, why they are needed, how they work, and what goes wrong.

Temperature & Pressure Relief Valve Inspection, Defects, Testing, Repair Q&A

These questions and answers about safety valves or TPRs or pressure or temperature relief valves were posted originally

at RELIEF VALVES - TP VALVES - home - be sure to review that material.

Does the relief valve discharge tube have to be of copper? Is PVC ok?

Thanks for the information. Is there any requirement that the fitting and pipe extension is required to be made from copper? I came across a boiler where the fitting off the T&P and the extension to the floor is made of PVC. - Kevin 7/26/2011

Reply:

Kevin the relief valve would itself tap into a metal fitting on the boiler or on older installations on metal heating piping.

But the discharge tube on many new installations is plastic; it's a pipe that rarely sees service and whose job is to divert hot water to the floor rather than onto a bystander. In that application most code officials accept PVC.

 

Leaks trickling out at new Gas Boiler Pressure Relief Valve

14 month old WH gas boiler (model # from sales contract WBRU**400** ; from user’s info manual WBU 80W/100w/120w/140W) leaking about 8 g water/day from PRV after replacing a radiator.

System was purged of air following the instructions in the manual and still is releasing water. System never leaked water until after this radiator was replaced. We have made other radiator changes on the system and followed the same procedures without having this issue.

Radiator changes are being made as we are in process on home remodel. One small rad was removed last year without issues. We temporary removed a radiator while demo-ing and redoing a bath in order to tile under rad. A copper pipe was installed in its place to keep the system running. We did not have any leaking. When the pipe was removed and the radiator re-installed after the work was completed, the PRV started leaking.

Following may not be related as this is the second time it has happened System displayed an error (E-10 Flame has extinguished 8 times) last year and after a couple days after new radiator was installed. Both times were after we had a warm day during typical NJ winter weather which also creates a moderately more humid basement area where the boiler is located.

After placing de-humidifier in the basement and temperatures dropped to normal (40’s) heater started working again.

The system was shut off (we were concerned about having damage to the controller if left on with error code.

We had these concerns as one controller had to be replaced within first year. We turned system on 1 day later when temp dropped over night and it started working again.

More water is being released since the system shut down then it did previously. We are able to measure the amount of water as we fill up a 5 Gallon buckets with it.

We fill 2 of these buckets a day about 3/4 full or so.

I cannot find any pressure valves to read and using the electronic display cannot figure out how to determine them. I did video the display when it called for heat. It may have turned on approx 1 min before I got to the heater. Temp initially read 137, dropped down to 128 then slowly increased to 190.

There is no Outdoor Sensor and system does not supply DHW.

There is no leak from the expansion tank (no name on the tank or model number), no leak from any of the values, no water that is coming out of the condensate line that we can tell (no ice on the ground outside where it drains and figured we should have some when temp are below 32).

Water coming out of PRV is like a faucet on very slow, but not a drip, drip, drip. More like a trickle. Have on video.

Have attempted to solve by reading many articles on this site and FAQ, but am a bit stuck. Also my eyes tend to glass over when I read a list of detailed instructions so I may have missed suggestions on a FAQ, but have tried to be thorough.

System is no longer under any labor warranty so that is why we have not had them out as we thought it was related to perhaps not properly purging air out of the system. We’ve called but they were going to charge and am probably being a bit stubborn as we’ve had problems with the installation since it was installed 13 -14 months ago,

but will definitively call if this isn’t something we can solve. We are a bit cautious in doing anything further as are concerned that we may damage the system in trying to solve this.

Should we try to purge the system again or could the PRV be damaged or not closing properly? (We would call a service tech to repair if that is the case)

btw have read all the links to a BLEVE explosion etc. If the advice is don’t touch it and call service tech, we will do that asap. If there are things we can try, we would like to, but will heed advice. On 2019-03-03 17: by Carla L -

by (mod) - leaky pressure relief valve is dangerous

Carla

Watch out: when a pressure relief valve is leaking the heating system is UNSAFE and risks a BLEVE explosion as you've read at BLEVE EXPLOSIONS

Clearly something was disturbed during the radiator replacement - that often requires draining the boiler and hot water piping system, and often someone may fool with the PRV to aid in that process; that in turn can disclose what was already present, a latent defect in the valve such that it is not fully closing.

Please review the causes and cures for leaky TPR valves beginning at RELIEF VALVE LEAKS

and at RELIEF VALVE, TP VALVE, BOILER

The cause may be a bad valve or boiler over-pressure or boiler over-temperature.

Your service tech needs to identify and fix the cause and possibly also she'll replace the relief valve regardless.

 

Water is shooting out of a valve at our well head.

Water is shooting out a valve on the well head in the front yard. What might be the problem - Sue 8/21/11

Reply:

Sue: regarding "Water is shooting out a valve on the well head in the front yard. What might be the problem"

Hard to guess intelligently with no information, but certainly yours is a well piping and pump question not a heating system pressure relief valve question (the article above on this page).

You may have a well piping leak - most likely, or on occasion a well casing leak combined with an artesian well. Take a look RELIEF VALVE, WATER TANK and also

at WELL PIPING LEAK DIAGNOSIS and call your plumber.

 

Pressure keeps going up in my hot water boiler - how do I diagnose this?

Hot water furnace. My gauge goes up to 32 pounds then trips. Shut of furnace and still happens. My hot water tank is heated by furnace. I shut off valves on lines going to my hot water tank and problem stops. Should I suspect internal leak in hot water heating core allowing internal pressure in tank to leak back to furnace causing pressure to rise. - Will 8/22/11

Reply:

Will,

If your heating boiler pressure is going up to 32 psi, a pressure higher than normal boilers heated to 180 or even 200 °F, and high enough to open the pressure/temperature relief valve, then I suspect:

- a tankless coil leak that is sending house water pressure into the boiler


or


- a malfunctioning automatic water feeder/pressure reducer valve feeding too-high starting pressure into the boiler


You can diagnose these easily enough.

Turn off the water supply into the tankless coil or water heater.

When the boiler is COLD, and assuming you've got a typical one-family home that is one or at most two stories, drain off boiler water to drop the starting pressure - cold - at the boiler down to 12 psi.

With the hot water system still turned off and the boiler left OFF you should not see any pressure increase inside the boiler. If you do, either we've missed something, or you've got a bad water feeder valve.

Then with the boiler turned on, the boiler should heat up to a temperature at or below 200 °F and pressure in the boiler should stay below 30 psi, probably around 20 psi.

Then with the hot water system turned on and the boiler COLD AND OFF (just for simplicity of diagnosis) and a starting boiler pressure of 12 psi, if you see the boiler pressure increase, you've confirmed a hot water system leak into the boiler interior.

 

Water heater pressure goes up too high and the TP valve opens

I have a water heating system with radiators and no tank. My pressure goes to over 40 psi and the safety valve opens. I touched the pipe going to the expansion tank and it's cold so it looks like no water goes in there when it should.

If I shut off the water supply line and drain some water the pressure reduces, however after draining it seems as the amount of water is not enough to go all the way up to the 2nd floor radiator.

I checked it by opening the bleed valve and nothing comes out since there is not enough water to fill it all the way up

. It heats great when the supply line is open but the pressure goes way over normal. Based on the scenario below I am suspecting a bad feeder/pressure reducer valve. Do you think this might be causing the problem. Any info would be greatly appreciated. Thank you. - May0 12/4/11

Update:

I ran a test for the feeder/pressure reducer valve and it's fine. It shuts off the water exactly at 12 psi. Once the systems turns on and starts heating the water, the pressure keeps rising way over 30 psi.

I watched it and it went over 40 psi when the water temperature was 150 F. I really don't know what might be causing it. I looked at the boiler unit and I can't see any signs of leaks. Shouldn't the expansion tank take care of this?

Thinking logically the water should escape there and therefore reduce the pressure in the system. I don't think any water goes in that tank.

I shut off the valve on the pipe going to the expansion tank. I drained it - there was hardly any water in there. I opened the valve and I was touching the pipe to see if it will get hot once the water goes in there. All this was done while the pressure was over 40 psi. The pipe didn't get hot making me think no water went in there.

After that I opened the drain valve on the tank and the water started coming out reducing the pressure immediately. What could be causing the pressure to rise so high? Is the expansion tank's job to at least partially help regulate the pressure in the system? Thanks for your advise.

Reply:

Mayo, the diagnostic procedure you need is at RELIEF VALVE LEAKS.

Also take a look at WATER PRESSURE TOO HIGH: DANGERS for some examples of causes of abnormal water pressure.

 

The pressure valve leaks when my boiler runs for a long time

I have a 20 year old SlantFin cast iron oil boiler. I have had 3 different technicians clean and set it up and I still have the same problem.

The pressure valve leaks pressure/water when the boiler runs for a long time.

When just using hot water or if only one zone calls for heat, it is fine. However, if multiple zones call for heat such as first thing in the morning when the programmable thermostats turn up, the pressure rises to about 30 PSI after about 10-15 minutes which is enough to make the valve open and trickle water. The colder it is in the house the bigger the puddle.

Any help or suggestions would be appreciated. - Tom Dionne 3/28/12

Reply:

Dionne, check the temperature on your boiler when the TP valve is leaking - if it is too high that could be the problem - fixed by adjusting or repairing the aquastat control. The diagnostic procedure you need is

at RELIEF VALVE LEAKS.

Also see WATER PRESSURE TOO HIGH: DANGERS for other causes and effects of of abnormal water pressure.

 

We hear a loud whooshing noise after we take a shower

After showers we hear a loud "ccssshhh" noise which sounds like it may be from the hot water tank. What could this be. It happens a couple of times after shower - Julia 8/21/12

Reply:

Julia, have someone standing at the water heater and other water handling equipment in the building so that first we know where the noise is coming from. That's the first step in diagnosing this problem. Otherwise an answer here would be just too-wild speculation.

 

I keep having to change my pressure relief valve due to leakage

I regularly have to have my pressure relief valve changed after a year or so because it starts to leak. My oil company says that happens with anti-freeze. Is there a special one to use with anti-freeze? FYI: I am on city water but do not have a pressure relief valve. - Mike 10/22/12

Reply:

Watch out: Balderdash. Either you're getting a series of defective TP valves installed (unlikely) or there is a cause of abnormal temperature or pressure at your heating boiler that needs to be properly diagnosed and fixed.

The diagnostic procedure you need is at RELIEF VALVE LEAKS.

 

What kind of pressure relief valve do I need on my water heater?

hi i have water heater 40000 btu natural gas what kind of pressure relief valve i need ? thank you - Paul 12/11/12

Reply:

Paul, the installation instructions for your water heater will tell you exactly what temperature/pressure valve is required for your unit. The specifications will include:

1. The BTU or heat release rate required - it will be a number typically above the BTUh input rate for your heater (that's probably your 40,000 BTUs, so the BTU rating of the TP valve will be above that number
2. The temperature operating range required - it will be a number in °F above the normal upper or hottest temperature that your water heater operates at - for example it might be set at 200F - certainly below boiling temperature.
3. The thread tapping size or diameter for the fitting into which the TP valve mounts - on residential equipment that's usually 3/4" though we see 1/2" IPT on some older units

Watch out: installing a TP valve that does not meet the water heater's specifications is dangerous and risks an explosion

 

Shouldn't I follow the manufacturer's instructions and test my boiler's TP valve every year?

I like this set of sensible and logical inspection steps. However, the Watts 374A 30PSI pressure relief valve clearly states on its paper owners/users tag atop the metal specifications tag that the homeowner should activate it yearly to ensure proper function.

I'd rather do what you are suggesting because it avoids the possibility of trapping any boiler water sediment/foreign material in the valve and preventing it from seating fully. But, wouldn't further 'flushing' of valve with more water usually rectify this? Like with Schrader valve with air in inner tube of bicycle tire or for auto tubeless tire valves? - Christopher 1/9/2013

Reply: better to ask your HVAC service tech to test the TP valve

Thanks for the good question Christopher.

Normally we always want to follow the product manufacturer's directions - they have a great interest in safe proper use of their equipment. And I agree that sometimes you can stop a leaky TP valve by repeated flushing of the valve to get debris off the valve seat. But I also have opened a TP valve to flush it and had the valve spit out part of the valve seat washer - leaving me with gushing hot boiler water at scalding temperatures.

The advice to "test" the TP valve by opening its test lever once a year is "safe" advice for the manufacturer to give. But it's not so safe for the homeowner because in my OPINION:

• If the valve opens and won't stop leaking you will have to shut off heat and wait for a heating service tech to come by to replace the valve
• If the valve is not properly piped with a discharge tube the homeowner may be scalded
• If the discharge tube just spills on the floor you're soaking your feet unnecessarily
• The homeowner does not normally stock a replacement TP valve nor know how to safely replace one that is leaking; that procedure requires shutting off the boiler, draining down some of its water content, then removing and replacing the old TP valve and reinstalling the discharge tube piping.
• Home inspectors are trained to never test the TP valve by operating the test lever because too many have opened a valve to have it fail to shut off - converting a latent problem into an immediate mess.

Therefore a safer suggestion for all homeowners is to ask their heating service tech to check the TP valve at the time of annual service. The service tech has a replacement TP valve right with him or her, in the service truck, and s/he knows how to replace the valve it if keeps on leaking.

 

Comment: relief valve drain froze leading to an explosion at the heating boiler

One danger (I may have missed) happened to me. The T & P valve had a slow leak which drained outside building.

At a persistent 4 degrees above 0 F, the water drip outside eventually froze and sealed the drain pipe at the exit point.

Once sealed the pressure built until the T & P valve exploded and the final six week repair cost came in at just over $36,000.

T & P valves are a real hazard to home owners! - B.T. 1/27/2013

Reply:

Excellent point; We've talked about the issues of draining to a remote or unobserved location, but not about the freeze risk. Thank goodness no one was killed.

Actually you are describing a triple fault that led to an explosion:

1. The TP valve was leaking - we don't know yet if the problem is the valve (replace it) or some other operating problem with the boiler (find and fix that cause)
2. The TP valve discharge was piped to a location where no one noticed the leak, so the root cause was not repaired
3. The water leaking through the TP valve discharge tube was at a low-enough temperature and slow-enough rate that when exposed to freezing conditions the TP valve discharge line froze, completely blocking the valve, preventing it from reducing boiler temperature or pressure

Had your boiler had a different weakest-link than the TP valve itself, the whole boiler could have exploded, causing still more damage and risking injury or even death to building occupants.

For example, had your device been draining a water heater the unit would become a rocket, shooting up through the building - details are

at BLEVE EXPLOSIONS.

 

The boiler does not have a pressure relief valve

First of all this site is amazing. The writing, pictures, and diagrams are everything I have tried to find online. My question is about an old hydrotherm gas boiler for a hydronic hot water system.

The boiler does not have a pressure relief valve and I could not a pressure overflow tank in the attic.

It is a 700sq ft. unit in a 4 unit house and the psi goes up to 50psi when the thermostat is raised above 80 degrees. I am obviously worried about this high psi. I have been lowering the temperature and releasing water to bring the psi down.

My questions are:

1. Can a pressure release valve be installed, if so where would it be installed?

2. A year ago one of the radiators busted and was replaced with a baseboard heater and that only heats up when the temperature is set high. One plumber said I should swap it out and that could fix the high psi issue, is there any truth to that statement? Does baseboard heat require more psi to heat up? (Jan 24, 2014) Rene

Reply:

Rene,

Watch out: It would be unusual (and unsafe) for a heating boiler to have no means of safety release of excess pressure.

If there is no attic overflow or expansion tank (or if not attic, in some other upper building location) and no temperature/pressure relief valve connected directly to the boiler, typically there would have been a red B&G or equivalent pressure relief valve installed on piping near the boiler.

See BLEVE EXPLOSIONS

Take a look at the pair of photos 9th down from the page top photo - where text below the pair of photos showing a red pressure relief valve reads

"This type of relief valve responds only to water pressure and may be located at some distance from the heating boiler itself."

You may find an equivalent installed on your system. That approach was common on older systems and was permitted then, though it offers less safety protection than a modern TP valve connected right on the boiler.

You can ask your plumber or heating tech to install a TP valve directly on the boiler only if the boiler includes an available tapping that would fit the valve, at a suitable location such that the valve's sensor is immersed in boiler water, and where the tapping is big enough (typically 3/4" dia NPT) to accept the device.

Send along some photos of your system and I may be able to comment further, but basically this is a safety topic to discuss with your heating service tech and the service manager.

No one in their right mind would leave a heating boiler with no pressure relief protection - the risk is a BLEVE explosion.

Regarding cold baseboard, perhaps the system is partly air-bound and could be corrected by strategic installation of air bleeder valves at the two ends of the baseboard run or at another suitable location.

(Jan 27, 2014) renetruj

Thank you DanJoeFriedman. How would I send you photos so you can see if I have a tapping to place a TP valve on this old hydrotherm boiler? Do you know of any sites that have a full listing of hydrotherm models, my boiler's plates and information are all missing or eroded?

Reply:

Renetruj

Use the CONTACT us link found at the top or bottom of any InspectApedia page.

About model identification, without the unit data tags you may be able to speak directly with Hydrotherm to ask for help - I would not want to guess based on just a box photo - since some boiler models may look alike externally.

 

The pressure relief pipe is dripping constantly

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. (July 21, 2014) Ian

Reply:

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.

Abnormally high pressure and relief valve leaks at OSB-4 Steam boiler - cracked "chamber" ?

I have an OSB-4 steam boiler. Once it starts, the pressure gauge rises to 10 or more then i am assuming that it's too much pressure the boiler makes a popping noise and steam escapes through the bottom of boiler.

I don't think the pressure relief vale was ever changed in close to 6 or 7 yrs and the pressure gauge in from of boiler as well.

I was told that the chamber is cracked, but if it was cracked my guess is that it would start leaking once its passed 5psi. I think they just want to change the boiler and make money. The boiler is 8yrs old. Anyone please advise? On 2015-03-24 by Will

by (mod) - unsafe, improper pressure, and possible boiler replacement needed

Will

Residential steam boilers usually operate at below 1 PSI. If the TPR valve is opening and the pressure is up in the 10 psi range the TPR is working as it should and your service tech needs to find out why the boiler pressure is excessive.

by Will

Thank you DanJoeFriedman. So then, the chamber should not be a problem due to that the popping occurs when it reaches 10psi or a bit more.

I have tried to view the pressure relieve valve to see if it opens but in my case it does not. I am not going to quote you on the broken chamber. Its that i am just trying to find out what is the most common issue regarding my issue. Changing the boiler i am sure you know, it costs and arm and a leg.

I'm not sure I understand "not be a problem" - abnormal heating system pressures are a problem and are unsafe. And there is a further risk that ultimately mineral debris and crud from the spilling relief valve cause that valve to stick shut and stop providing pressure relief - risking a boiler explosion.

It's a big and probably unnecessary leap to go from needing to find and fix the cause of a flooding steam boiler to the claim that the boiler needs to be replaced. If your on-site heating service tech says you need a new boiler ask him or her to explain why - there should be good reason such as actual boiler damage that is too costly for economical repair.

by Will

I tested it out earlier and at 15 psi is when the steam/vapor comes shooting out from the bottom. It does not look like the pressure release valve is working. I was told to change it and put a lower psi release valve. I am hope that would would help. As of right now i turn it on and shut it off at 10psi before it hits 15psi, cause thats when it leaks, does this make more sense?

No it does not make sense to me. Installing a lower pressure release point valve will hardly fix the cause of boiler overpressure.

I repeat that what you describe is unsafe and needs an onsite professional.

by Will

Ok will do DanJoeFriedman, thank you for all of the advise, just one last question, from what i described does it sound like the chamber cracked? To me something is clogged. i will have an expert look into this, i just don't and really can't afford a whole new boiler whether it's new or refurbished.

Good going, keep me posted.

As I said, if you are told you need a new boiler, ask for details and ask us for comment.

by Will

I will i promise, its just that i have a gut feeling they are lieing just to make money.

I do have experience in working with temperature chambers on pressure transducers for military etc.... and in my opinion if you have a completely sealed chamber and pressure builds beyond what it's design for, of course that baby will blow, but if the chamber was cracked my floor would be filled with water or even when the pressure of the chamber is at 10psi.

It just does not make sense to me. At 15psi is when it pops or begins to leak steam, "NOT WATER" but steam, its like something is stuck.

I will keep you updated. Thats why i slightly very slightly left the pressure valve opened just a bit to test out the duration of the chamber leaking or steam escaping and it did take longer. I will keep you posted. Thanks again!

Will

Watch out: You're discussing a steam boiler. You have described an unsafe condition. You need to call a steam heat service technician.

There is no reason to start assuming that you need a new boiler, and no reason to use that worry to hesitate to call for proper repair. Your delay risks costly boiler damage or even an explosion.

DO NOT leave a TPR valve propped open - doing so is unsafe. The continued venting risks clogging the valve with mineral deposits leading it to fail to open properly when it should - again risking a BLEVE explosion.

On 2015-03-27 by Will

Ok DanJoeFriedman, will do what your recommending. I think a guy is coming this week. I will keep you posted. Thank you!!!!

by Will

Good morning everyone, Dan its confirmed, actually i saw it dripping from the bottom. Had to drain it, mop the freaking floor and shut all valves.

by (mod) - Call your heating company for more prompt service - a dripping pressure relief valve is unsafe

Watch out: You're discussing a steam boiler. You have described an unsafe condition. You need to call a steam heat service technician.

by Will

Yes i just spoke with them and they are going to change it. Dan it was a battle, i was trying to resolve this cause i really did not think the chamber was cracked, but hey, things happen and when it's in areas that the human eye can not see, thats when the surprise occurs. I thank you so much for trying to guide me here.

Expansion tank valve is closed to boiler and relief valve leaks

Hi, I recently had my heat repair guys at our house to fix a radiator valve leak and just the other day I noticed that our relief valve is draining water (about a gallon or more a day) while the boiler is running. I also noticed that it appears the valve to the expansion tank is closed--could this be the reason that the relief valve is opening? On 2014-12-21 by Chris

by (mod) -

Chris, there may be more than one valve at an older style expansion tank - one to isolate it from the boiler (normally open during heating) and another to drain the tank. If the tank is isolated from the boiler it's like having no expansion tank and the TP valve would likely dump at every heating cycle.

 

Relief valve Drips at Lennox Conservator Boiler - how do I stop it?

Great site....
I have a hot water boiler (Lennox conservator) and just recently the relief value started releving (dripping) at about 175C temperature about 27 psi.
The valve states 30 psi and 535,000 btu hr


The furnace states input 105000 btu hr
Min relief valve cap 85 lbs/hr
The thermostate on the furnace is set at 150

How do I make it stop?

Thanks!!! On 2014-11-02 by Relief valve Drips

by (mod) -

Easy RV

at RELIEF VALVES - TP VALVES - topic home - there is detailed advicve

Typically we replace the valve and also diagnose and fix the cause if the problem is not the valve itself. Causes of to valve leaks are in the cited article.

Watch out: a dripping pressure relief valve is potentially unsafe, risking a boiler explosion.

Get help from a trained heating service technician promptly.

...

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

Or see these

Recommended Articles

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

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