Water heater T&P Valve installation (C) Daniel Friedman Temperature & Pressure Relief Valve Diagnosis
Diagnostic FAQs - Questions & ANswers

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Water heater safety valve diagnosis:

Diagnostic questions & answers for TP valves or relief valves used on water heaters, boilers, other water heating devices. Why is my TPR valve leaking? How do I pipe the temperature / pressure relief valve discharge tube? Why is my T&P valve dripping and what are the relationships among building water pressure, water hammer, water temperature, and dripping or spilling T&P relief valves.

Reader questions and replies to them can help figure out what's wrong with the TP valve on your heating boiler or water heater.

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Temperature & Pressure Relief Valve Questions & Answers

TP Valve installation schematic - American Water Heater Co.Some of the FAQs discussed below are adapted from information provided by the Watts Regulator Company in "52 Questions and their Answers", Watts Regulator Corporation (1973) [10]

Question: Leaky pressure relief valve blamed on bad expansion tank bladder ?

I have a weil McLain hot water boiler, which is about 20 years old. It was leaking out the pressure relief valve, so we changed out the expansion tank which had a bad bladder in it, as well as the pressure relief valve, but now I noticed it has continued to leak out of the new pressure relief valve when the boiler is running. Any ideas? - Vincent Nizzardi


A bad expansion tank bladder would certainly be a cause of relief valve leakage. As you replaced both the tank and the TP valve, and now see a leak at the new valve, there are other possible explanations such as:

Keep us posted - what you learn may help other readers. - Editor

Question: Do I also need a TP valve on the cold water line? What about a check valve on the cold water supply main line?

Do I need a pressure-relief valve on the cold waer pipe that feeds my hot water heater tank? - Watts

Do I need to install a check valve on the cold water supply main line? Is it safe to do so? - Watts

On a municipal water supply system, do I need a check valve on the cold water line if a TP valve is installed on the water heater? - Watts

Reply: no

No, there is no need for a separate pressure relief valve on the cold water line feeding the water heater. That's because water pressure within the system is common throughout all of the plumbing system: cold water line into the tank, hot water in the water heater, and hot water in the hot water lines leaving the water heater tank all see the same pressure. [10]

... the original purpose of a check valve was to protect the [water] meter by preventing superheated water from backing up into the cold supply main from range boilers and heaters. However, the very condition that can cause this, can also cause explosions and the temperature and pressure relief valve principle protects against both excessive temperature and [excessive] pressure, thereby eliminating the need for a check valve. A check valve closes the [plumbing] system, thereby allowing pressure to build up from thermal expansion higher than the city main pressure, and therefore should not be used except where required by local codes. [10]

Note: We add that there are other reasons for a check valve or backflow preventer valve on water systems: to prevent water from the building from flowing backwards into the city supply mains during an interval of loss of pressure in the mains. Should such a pressure loss occur the risk is that unsanitary water from buildings connected to the mains could flow backwards into and thus contaminate the water supply mains in a community. Most community water supply systems include a pressure regulator combined with a backflow preventer or check valve at the water meter. Watts' note above was penned in 1973. The company may have more to say on this topic today.

When a hot water system includes a temperature & pressure relief valve installed on the water tank or heater there is no advantage to installing a check valve to protect the water meter - as Watts explained in the quotation above. Watts points out that if a check valve is installed on the cold water line to the water heater, a result is a pressure rise in the system each time water is heated in the hot water tank.

Question: What is an "open main" water system and does it have safety implications for water heaters?

Does the water pressure in my house plumbing system ever increase under any circumstance (hot water heater or something else) on an open main water supply system? - Watts


In an "open main" system nothing is closed between the house [plumbing] system and the street main. Therefore, water pressure [in the house] cannot increase above the street main pressure from the reservoir regardless of any expansion [in the hot water system] from temperature. Consequently, a straight pressure relief valve cannot operate unless a system is closed.[10]

Note: By "straight pressure relief valve" we think Watts means a valve that responds only to water pressure and that does not include a response to hot water temperature. Such a system could be unsafe.

Question: Why is hot water pressure going up to 150 psi in my water heater tank?

I had to install a new temp controller in my hot water tank. It is a bourdon tube type and I installed exactly like the original one. The water in the tank is heated by a coil as a separate zone from the furnace. The house water pressure is about 50 psi. I have the tank temp set at 125 degrees.

I installed a pressure gauge between the pressure relief valve and the top of the tank. When the hot water from the furnace enters the tank the water pressure goes from 50 psi to 150 psi and the relief valve discharges a little and then stops. The water temp is 101 degrees at this time. Why is the hot water tank pressure increasing to 150 psi? - Alan


Alan you may need an expansion tank on your water heating system. Heating water in a closed container increases the pressure. See our discussion above about Closed Hot Water System & Thermal Expansion Problems.

Question: can I use a combination of check valve and pressure-only relief valve to protect against overheating my hot water tank?

Will a "straight" pressure-only relief valve prevent overheating and thus keep my hot water system safe if a check valve is also used?

Reply: No. Such a system is unsafe

No. Overheating in the hot water system depends entirely on the BTU input rate to the water heater. A relief valve that operates on pressure only (ignoring temperature), regardless of its size or rated discharge capacity, can't prevent overheating nor reduce temperature. Such a sysetm is unsafe.

Question: will the relief valve affect building water pressure delivered to faucets?

Can the relief valve affect the pressure of water coming out of faucets? - Pam Gregg


No, Pam, not under normal circumstances. That's because hot water leaving the water heater may pass BY a relief valve en route to your faucets (depending on where it is installed) but the water is not passing THROUGH it.

But if a water heater pressure-relief valve were stuck wide open flushing hot water continuously down a drain, building water pressure would probably fall noticeably - that would be an unusual circumstance and surely you would know it, from the flooding water out of the valve and quickly by the loss of hot water.

Question: using the "easing lever" on TP Valves? When should a TP valve be replaced?

Constricted relief valve (C) Daniel FriedmanI don't understand how simply lifting the "easing lever" verifies that the temp./psi. relief valve is intact and will function properly at factory set limits. Most water supplies have trace elements , including some non- toxic metals.

These elements usually collect and build up on the sensing stem of a water heater relief valve. If a relief valves "easing lever " is tripped, valves with lime and trace metal accumulation often will not re-seat, resulting loss of heated water,shutting off the water supply to the unit, shutting down the power to the unit, ordering a new relief valve and installing the replacement. It's seems to thoroughly test a water heater relief valve, Psi. and temp. limits would have to applied that would require the relief valve to engage.

Once a relief valve has released at its set point it should never be put back into service. - Ken Hansen

Question: since a TP valve releases excessive pressure in a water heater or boiler, isn't pressure-release enough protection against a water heater tank explosion?

If the condition of too much hot water pressure is corrected by the automatic opening of the pressure/temperature relief safety valve or "blowoff valve", why was I told that a water tank can still blow up?

Reply: relieving pressure alone won't prevent a hot water tank from exploding - that's why a TP valve also responds to temperature and the TP valve has to release heat at a rate equal to or greater than the BTU input rate for the water heater

One would think that the TP valve alone would always be enough protectin on a water heater tank. But as Watts Regulator Company explained back in the 1970's and as was demonstrated in the film "Explosion Danger Lurks", even a wide-open pressure relief valve can not prevent water in a water heater tank from becoming overheated.

At WATER TANK PRESSURE CALCULATIONS we discuss the calculations behind the increase in temperature and pressure in an enclosed water tank or water heater tank. In the case of a hot water storage tank, Watts points out that

The reason that the volume of pressure discharge [through the relief valve] is not enough to overcome the BTU heat input [into the hot water heater tank] is because thermal expansion pressure is approximately 2 1/2% of volume for every 100 degree rise. [The] fluid heat discharge ... necessary to relieve the extra BTU heat input for every 1000 heat units is about 20 times greater in volume.

In a [hot water heating] system with a check valve and a pressure relief valve, the relief valve opening by pressure increase due to expanding water will discharge approximiately 1/2 lbs. of water for each 1,000 heat units (BTUs) put into the water - because that is the rate at which the water expands when heated.

To release 1,000 heat units when the temperature is at 210-212 degF, there must be approximately 6 2/3 lbs. of water released from the system. In other words, to prevent overheating [water in the hot water storage tank] a means must be provided to relase about 20 times as much water from the system as a pressure relief valve can discharge from thermal expansion [alone], when there is a check valve in the supply line or [when there is] an accidental stoppage [of the water piping] to make the system a closed one.[10]

In other words, in a closed hot water piping system (closed by the presence of a check valve or a blockage in the water piping to prevent expanding hot water from "pushing" water volume back out of the watertank, to prevent a hot water tank from overheating, the TP valve has to discharge heat [not pressure] at or greater than the rate that the heater's burner or electrodes are putting heat into the water in the tank.

But on a typical water heater, the heat input rate in BTUs is about 20 times more than the heat output rate through a TP valve if it operated on pressure alone.

Watch out: the conclusion of this technical discussion is that it is absolutely essential that the BTU (heat or energy) dumping rate for a TP valve must be properly matched to the BTU input rate of the heater. And a pressure-only relief valve on a water heater, that is excluding a valve that also responds to temperature, would be an unsafe installation.

Question: figure out this relief valve problem

(Feb 20, 2012) Jeff Garmel said:

I had a new water heater installed. It leaks at the relief valve. There is a 10-15 year old Amitrol Therm-x-trol ST5 (2 gallon) expansion tank on the cold water line before the heater. is it possible that the installation drained the air out of the tank? thanks Jeff

(Mar 7, 2012) Sunil Jay said:

Water is leaking from the bottom opener near electric connection. Is it through the heating element bushes

(Mar 7, 2012) said:

Very fast and reliable guidance. Thank you.

(May 26, 2012) pam said:

there is water coming out of my hot water heater and it's making a funny noise the water is turned off and so is the gas



I have found that leaks anywhere in a water heater will often appear as both water on the floor and water appearing at the water heater tank metal jacket bottom and vertical sides around the heater base where there is a sheet metal seam. In other words the leak may be from somewhere higher up. You should not try to remove the heater jacket, but you can remove the covers over the electrical water heater controls and elements (if yours is an electric heater as your message suggests). That will give view of the mounting of the two heater elements and you will see directly if the leak is from one of those locations.

Send along photos if you like and I can comment further - use the CONTACT links found at page top or bottom.

(May 29, 2012) (mod) said:

Pam if the water is leaking out of the heater itself it's probably time to replace it.

Question: is a TP valve required on a wall mounted water heater?

(Oct 2, 2012) Bill Miller said:

Is there a rule or code on how many 90 degree 3/4" fittings can be used on the drain line of a T&P at a 75 gallon State water heater?

(Oct 4, 2012) James said:

IS a TP valve required for storage wtaer heaters that are wall mounted, 50 liter capacity. I ahve noted that most household storage water heaters in the middle east have on TP valve except a releif valve on the water INLET of the heater. Yet all these are listed and registered to be complying with the IEC 60335-2:2002 Household and similar Electrical appliances: Storage Water heaters? would appreciate guidance. cheere


James a temperature and pressure relief valve is required on any hot water tank or cylinder regardless of how the tank is mounted.

James, yes. I worry that a relef valve on the cold inlet is not what the manufacturer specified, and that even if it responded to overpressure it won't respond safely and reliably to an over temperature condition.send us brand and model numbers for research.

Question: tested the TP valve now it keeps leaking

(Dec 2, 2012) Sun said:

After lifting the lever of temperature and pressure relief valve for annually maintenance,hot water leaking for hours, I wonder when its stop?



Tap gently on the pin that pulls the valve open. If that doesn't reseat the valve, and if flushing the valve doesn't remove debris from the valve seat it's time to replace the valve.

Watch out: a temperature/pressure relief valve that keeps dripping is unsafe and could risk becoming clogged, failing to open on overpressure and leading to a dangerous or even fatal boiler explosion.


When in doubt replace the valve. You should be using a heating service professional.

Also check for abnormally-high system water pressure and water hammer problems in the building.

Question: Thermal expansion valve on cold line leaks

(Dec 22, 2012) charles said:

I have a thermal expansion valve that is installed on my inlet line (cold water line going into my hot water tank) that is leaking, now the question that I have is, is it required to be on the inlet line . Talking to a few friends that do plumbing and they are saying that it is not required, but they recommend that I install a expansion tank.

So, another question is if the system was installed without a expansion tank is it a good idea to install one are just replace the thermal expansion valve that was installed when the hot water tank was installed, are just remove the old system and install a new hot water tank system per new system directions ? So many questions, but can't find all the answers! NEED HELP !


Sounds like you need an expansion tank but first I'd check for any other sources of abnormal system pressure such as water hammer.

Question: Rheem PVW50 TP valve leaks

(Jan 11, 2013) Wayne said:

I have a 9 year old Rheem PVW50. Last year I replaced the drain valve, T&P valve and the anode rod. The old anode rod was worn out. A couple of months ago I noticed the T&P valve was leaking every once in a while. Then it started every day.

I read an article that said if the T&P is leaking to open the cold water faucet, if the T&P stops dripping it is not the water heater. But to check it out get a watts gauge with high pressure marker. So I purchased one and found out the cold water was going up to 110 psi and hot water heater up to 150 psi. Found out I need to replace the Watts Pressure Reducting Valve AU25B.

After replacing valve cold side is now 50 to 60 psi. However, the hot water heater registers 50 to 60 and when the water is being heated may go up to 100 psi. No water is leaking out of the T&P valve or anywhere else. Putting my ear to the heater I can hear a little grumbling out of the tank but not overly so.

So my question is 2 fold. First, is the water pressure of 50 to 100 in the tank ok? Secondly, when is the best time to replace the tank but still get maximum usage out of the water heater? I've been told by a friend at Rheem that they have seen 15 to 20 years out of the tanks.


Opening a cold water faucet isnot a proper fix for a leaky TP valve. Replace the valve; if the new one leaks check the system temperature and pressure; Your system may need a hot water expansion tank.

Question: Nipple between water heater and TP valve

(Feb 12, 2013) Ethan said:

Hello! I have a question here, not addressed by any web info I can find:

Is it against any code to have a nipple (about 1" long) installed in between water heater and the T&P valve? (instead of having the T&P valve threaded directly into the tank). I'd rather not use an extra-long T&P valve. Much thanks!


In my OPINION the installation you describe is improper and unsafe and if it violates the manufacturer's installation instructions, indirectly by that error it's "against code" as you put it.

The short nipple you describe raises the valve, reduces the depth of extension of its temperature sensor into the water heater, so is improper.

Question: O ring blew in mixing valve - is there a sticking relief valve problem?

(Mar 4, 2013) ron goodrick said:

hi there just replaced an expensive basin mixer cartridge leaked installed new one .. 3 days o ring blew in hose //sticking temp relief valve ? dodgy taps ??

Mar 6, 2013) SOMIDI MAHESHWRA said:

IF A SAFETY VALVE IS GETTING RELEAF AT 250 Deg centigrade and presuure 20 kgs/sq cm if my temperature is 30 deg centigrade what is the pressure of release in kg/sq cm.


These questions are a bit unclear leaving us reluctant to guess at an answer.

Watch out: if your TP valve is "sticking" - that is not opening when it should, the system is unsafe. See BLEVE EXPLOSIONS

Question: Washing machine blows the TP valve

(Mar 16, 2014) mike said:

I have a front loader washing machine and it blows the T&P Valve on my electric hot water tank. Any solution on how to fix this problem. I have put in a pressure reducer coming into the house and water hammer behind the washing machine and nothing. Should I replace the T&P valve again since it has blown 50 plus times. Only with the washing machine nothing else it blows


I'm unclear how the washer is causing the TP valve to blow or leak - and because there could be a very serious safety hazard involved, some accurate diagnosis is in order.

For example, if the problem is due to water hammer caused by the washer operation, there are water hammer control devices you can install at strategic locations on the system to solve the issue - search for


But if the washer cycle is for some reason causing the hot water source - a water heater - to overheat or malfunction, that could be a serious safety hazard.

Question: new TP valve for new water heater?

(Mar 29, 2014) henry parker said:

when I buy a new water heater do I also need to buy a temp relief valve?


Absolutely, if a TP was not included with the heater. Be sure to buy the proper valve matched to the water cylinder (heater) capacity and design and mount location.

I would never risk re-using an old TP valve on a new heater.

Question: why is just one TP valve leaking?

(Mar 29, 2014) C. David Hensley, said:

30 gallon water heater less than a year old with pop-off value leak, I have replaced the value, city water pressure is 40 -45 lbs., heat controls on 120 degrees top and bottom, this is the only water heater out of 12 apartments in the same building that leaks. What happen?


C. David,

You want to diagnose the reason the valve is leaking. In the More Reading links above click on


Question: constant discharge or leak from pressure relief valve

(Apr 20, 2014) John L said:

I had my hot water heater pressure relief due to a constant discharge of water. The plumber said the seat had worn over time allowing water to bypass. A few days later...leaking again. Checked the pressure on the water line closest to the meter and got a reading of 80 psi. Installed a pressure regulator set it at 60 and one day later relief still has a intermittent discharge, the water thermostat on the heater is set to normal and I pulled some hot water directly form the heater and it tested at 120 degrees.

What other problems could cause this? I have just paid this plumber $500.00 and still have the same problem. I am in the hydraulic industry and very well understand pressures and flows and never did believe a relief set at 150 psi would open at 60 psi.


John I don't understand the 'worn seat" in a temperature/pressure relief valve - but then I'm not on the scene. The valve does not normally open nor cycle open and shut so "wear" ought not to be a factor.

It is the case however that when someone messes with a TP valve it can open and then fail to shut - e.g. if debris then enters the valve seat or if its gasket blows out at that time.

More likely there is a cause of overpressure that needs to be found and corrected. You may need a hot water heater expansion tank. If the incoming water pressure is within normal ranges (80 is a bit high - about 10 psi over what I'd recommend but alone not likely to explain the issue you are having), and if the water heater temperatures are within normal range (where you tested is of course at a lower point than in the heater at the temperature sensor but 120 is well below the opening temp of around boiling) then the problem is elsewhere.

Question: can't test the relief valve - it won't open

(May 2, 2014) Anonymous said:

I tried to open the pressure relief valve on my water heater and It won't open by my hand and I don't want to use a wrench or pliers to force it. How should I get it open. It has been 7 or 8 years since it was installed.
there is no visual corrosion.


Good question anon.

Watch out: IF the test lever is stuck this is an important discovery, as it quite possibly means that the valve opening mechanism is stuck as well - that would be very dangerous - should an overpressure occur and the valve fail to open as it should the water heater becomes a rocket or a bomb. (Search InspectApedia for BLEVE EXPLOSION)

And if you use a tool to force the valve open there is a risk that it won't close and you'll have a flood.
And you'd risk damaging the valve (as you understand).

I would replace the valve.

Question: water heater whistling noise

(June 11, 2014) jane said:

My water heater is making a loud (very loud) whistling noise- my water heater normally makes loud banging noises and loud gurgles and popping sounds- I called maint- they said it is "normal" - the water heater is 12 yrs old and as he puts it "everyone's does that" - but the last time it whistled- we ended up having no hot water and they had to replace the element. My question is this- will it leak or explode and is there a auto shut off when the pressure gets too high and causes it to whistle? Will the gas leak and will the water leak out of the tank in the next 24 hours? I have kids and animals in the room with the water heater. It should be outside like most apts- but they have it in the bedroom and it's not safe.

PS- now there is NO noise coming from the water heater- and there is always some type of noise - so now it really makes me nervous and it's 12 am. I'm afraid to take a shower in the morning for fear of the water tank blowing up.



Watch out: Installing a gas fired water heater in a bedroom is unsafe and is prohibited by code, whistling a tune or not.

Question: Water heater in a cupboard, TP valve dripping

(June 23, 2014) Noel said:

With a hot water system located inside a cupboard what do you do with the "drip drip drip" coming with pressure relief? Is it simply dropping onto carpet?



Watch out: FIRST you are describing an UNSAFE CONDITION - a dripping relief valve ultimately clogs and stops dripping - at which point it also is no longer protecting the building from an exploding water heater.

So the cause of the trouble needs to be diagnosed: a leaky TP valve, overpressure in the system, overheating at the water heater, or water hammer or some other cause.

Do NOT simply route the dripping valve to a disposal location that is no longer visible or in the future the dangerous condition might remain undetected. (search for TUNDISH to read about a solution).

Temporarily, put a bucket under the end of the discharge tube so you're not also flooding the floor.

Then call a plumber to diagnose and fix the trouble.

Question: What is the overhead clearance space required for a TP valve installed on a water heater top?

Julie said:

I have a hot water heater with the temperature relief valve on the top. It is a short 30-gal water heater that is under a counter top. What is the minimum clearance distance that is required from the bottom of the countertop to allow the temperature relief valve adequate clearance? Is there a code spec for this?


Julie a look at installation details for TP valves on water heaters didn't come up with an over-head clearance, though some common sense would indicate you'd need enough space for the test lever to be operated AND enough space to remove and replace the valve when needed. Since a top-mounted TP valve has a temperature sensing stem that protrudes downwards into the water heater the removal space will be more than you think

On a small water heater (cylinder) the extension of the sensor is about 3" while on larger water heater cylinders that added length could be as mmuch as 9" below the inlet. Adding that 9" of sensor to the TP valve body and lever height (anywhere from 5 5/8" to 9 1/4") means the minimum (for the smallest valve size) valve total length is about 9" and the larger valve could be much larger.

Now we can slightly tip a valve to get it out of the heater, buyt - I'd like to see 12" or more to give both working space and space to remove the valve.

Question: electric water heater with too much water into the discharge tube

(Nov 25, 2014) K Young said:
My electric water heater experiencing too much water discharge into the discharge tube. I called in a plumber and he adjusted the control with his tools which stopped this bypass problem for a few weeks. I am not sure if this is due to problem with the p-trap valve or tube. The plumber had tested the pressure and it is good. My water heater is just 3 yrs old. Thanks for advice.



Your hot water heating system may need its own expansion tank.

See for details.

Question: Pressure and temperature on a 30 gallon Rheem temp press safety valve?

(Nov 27, 2014) Anonymous said:
what is the limits of pressure and temperature on a 30 gallon rheem temp press safety valve?


Anon I can't guess from just your question - we don't know fuel, btu input rate of your water heater, type of heater - nada. In general the pressure/temperature relief valve on any water heater will open at a pressure low enough to protect the tank from a BLEVE explosion (discussed above) AND/OR at an abnormally high temperature (e.g. over 210F) but the TP valve also must be sized to be capable of dumping hot water and/or steam fast enough to exceed the BTU input rate of the heating appliance.

Question: How do I add a water heater TP valve

How do I add a water heater TP valve - there's none on my heater


There should be a tapping on the upper side of the heater intended to accept a pressure/temperature relief valve. Be sure to install a valve with the proper capacity matched to the unit's input BTUH.

(Dec 30, 2014) Anonymous said:
Well, there is a plastic cap on the edge of the top, but when it is removed, there is only yellow styrofoam insulation under it.


I'd ask for help from a plumber to find the tapping and install a TP valve. You may need to remove insulation to expose the tapping and plug in that threaded opening.

Question: Replaced the T&P valve, new valve still discharged water

(Jan 10, 2015) Anonymous said:
We have well water, we have very little water pressure. We came home to a t&P valve violently discharging, called Rheem they advised to buy new valve and replace--gave us no instructions-- We just slapped a new one on turned the cold water back on and then immediately followed turning back on the hot water heater the new valve discharged a gushing stream. Called Rheem again and they said oh no there are steps that must be followed, so we drained the hot water heater and started "Fresh" and followed the steps to a "T". Now the T&P valve leaks it possible that all that monkeying around the first time ruined a brand new valve?


I'm not sure what might have happened to the valve - it could have been damaged or improperly installed.

But make a check of the system water pressure to see its level is abnormally high - if water pressure is above the TP valve pressure (or if you bought the wrong type of TP valve) that could be the trouble.
(don't confuse poor or slow flow with low pressure)

Water hammer an also cause a TP valve to leak but that leakage is not usually continuous.


Question: TP valve keeps spilling - should I turn off the heater?

(Jan 25, 2015) Juanita said:
I heard a noise coming from my AO SMith compact water heater under the sink and the T&P valve is turning constantly. I do not want to touch it and the repair person can not coming for a couple days. Should I just turn it off?



The system you describe is unsafe and should be turned off. We can't know if the problem is a leaky T&P valve or a problem with the water heater and overheating.

But since an overheated water heater can explode causing a dangerous BLEVE explosion you should TURN OFF THE HEATER immediately.


Question: Up and down pressure relief valve piping

(Feb 18, 2015) Kev said:
Can you run a pipe down then back up off a pressure relief valve



No that's dangerous and prohibited. Up-piped TPR discharge piping can hold water in the line causing the valve operating mechanism to clog with minerals or debris. The risk is a BLEVE EXPLOSION.


Question: Solar water heater problems

10 March 2015 David said:
Hi My hot water system is solar on roof with a 300 lt tank the tank is dumping its full content about the same time everyday the water is coming from the copper pipe on the wall


What pipe? overheating? discharge on the TP valve?

Question: Can 3/4-inch flexible copper tubing sections (with FIP ends) be legally used in any part of a water heater's T&P discharge line?

13 March 2015 Stan Stan the Inspector Man said:
Can 3/4-inch flexible copper tubing sections (with FIP ends) be legally used in any part of a water heater's T&P discharge line?


Thanks for the excellent question, Stan.

In a photo above on this page you can see a flexible 3/4" copper tube used in the routing of the discharge of a TP valve from the top of a water heater. No one called out the use of that piping material itself as a hazard, but there can be hazards nonetheless depending on how that tube is routed - such as to a hidden location without a Tundish or routed "up" from the TP valve itself.

So ... it depends. If for example someone installed a flexible line to replace a straight downtube running down the side of a water heater from the TP valve, I'd be worried that some fool would come along and bend the tubing "up" - as nothing prevents them from doing so. Maybe to get it out of the way of a basketball or something. The result is a dangerous blockage of the TP valve and the risk of a BLEVE explosion. SO if I I were a building inspector given final authority I'd object to that installation. But I might not object to use of the same tubing connecting properly beween a valve's discharge opening and a proper destination.

Quoting from Watts:

Discharge line must always be installed to avoid water damage and scalding injury, when valve operates. Discharge line must be same size as valve outlet, be pitched down for free draining, and have no shut-off valve or obstructions throughout its entire length. Discharge line termination point should be visible to observe any discharge.

Nothing in their installation instructions prohibit use of flexible lines per-se but in summary, it is certainly possible to find two violations:

1. the flexible line, if not connected at both ends, could be bent "up" causing an unsafe condition

2. it is not permissible to terminate a TPR valve discharge line with a threaded fitting - the reasoning is that it's too easy for someone to screw a cap onto a dripping line, leading ultimately to a BLEVE explosion.


Question: what is the cost to change a TPR valve in a water heater?

(Apr 6, 2015) Jayant Bakkshi said:
What is the price range for changing a prv in a Racold 20 litre storage water heater?



TPR valves are typically priced in the $10 TO $20. U.S.D. Range for the part. Plumbers charge by the hour, some plus travel and have fees that vary quite widely depending on where you live. The rate is often between $75. and $150. USD. Then, your question presumes that the changeout is straightforward and no unusual difficulties are encountered.

Question: does pressure relief valve piping affect water heater operation?

(Apr 16, 2015) Dave K said:
I have a question about the pressure relief valve piping. I completely understand the function and operation of the relif valve. I am in the middle od disputing a denied claim with a Home Warranty company who is trying to tell me thet the water heater does not operate properly with the piping being pointed toward the floor.

So my question is: does the piping on the pressure relief valve effect the operation of the water heater. Is there somewhere that documents that although this may be a safety issue, the water heater still will function.



Watch out: The TPR valve (and its discharge tube piping) MUST be pointed down for proper, safe operation. You'll see this in the valve installation instructions dpfrom the manufacturer as well as in researched articles found here. Pointing a tp valve up is improper, risks clogging, failure, and a catastrophic BLEVE explosion. If your insurance company says the valve should not point down you are welcome to quote me as observing that they are dead wrong and at are risking killing someone.

Question: relief valve leaks after changing to city water supply

22 May 2015 Gary W Barbour said:
I have a friend who recently switched from well to city water, and now her TP relief valve is leaking. she says it starts before it reaches temperature. she has already replaced the valve. and she didn't vent the air the first time she filled the tank. I suspect either she needs a pressure regulator from the city water pressure, or, and I don't know if this is possible, but its an electric water heater and because it wasn't vented when she filled the tank an air pocket could have let the top element burn out, and it is possibly creating electrolysis offgasses causing a pressure buildup.


Interesting thoughts, Gary. I've not considered troubles with burning out an upper electrode when re-filling an empty water tank. It'd be easy enough to test. See


It would be no surprise if higher city water pressure was causing a water hammer problem OR an over-pressure problem that was causing the TP valve to leak.



to actually measure the building water pressure. If the incoming pressure is over 70 psi I'd certainly want a regulator installed.

Keep us posted - what you find will help other readers.

Question: Water heater TP relief valve leaks after switch from well to city water

(May 21, 2015) Gary W Barbour said:

I have a friend who recently switched from well to city water, and now her TP relief valve is leaking. she says it starts before it reaches temperature. she has already replaced the valve. and she didn't vent the air the first time she filled the tank. I suspect either she needs a pressure regulator from the city water pressure, or, and I don't know if this is possible, but its an electric water heater and because it wasn't vented when she filled the tank an air pocket could have let the top element burn out, and it is possibly creating electrolysis offgasses causing a pressure buildup.


Interesting thoughts, Gary.

My first thought was that incoming city water pressure may be higher than what the well water system delivered, and that perhaps the pressure regulator on the city water supply is not properly adjusted. Start by testing the building water pressure to see what youv'e got. Higher than 70 psi is likely to cause leak trouble.

I've not considered troubles with burning out an upper electrode when re-filling an empty water tank. It'd be easy enough to test. See


It would be no surprise if higher city water pressure was causing a water hammer problem OR an over-pressure problem that was causing the TP valve to leak.



to actually measure the building water pressure. If the incoming pressure is over 70 psi I'd certainly want a regulator installed.

Keep us posted - what you find will help other readers.

Question: locating the water heater TPR valve on the heater top vs on the heater side

(Aug 3, 2015) glenn said:
water heater relive valve on side of water heater needs to be put on top of water heater so it flows down is it hard to change it to the top of the heater so it flows down the out side to the out side of the wall



Watch out: you should never pipe the TPR valve "up" at any point;

1. The valve must be mounted on the fitting provided on the water heater as otherwise its temperature sensor won't function properly.

2. The piping must flow only downwards from the valve mouth, otherwise the risk is ultimate clogging of the TPR valve and a BLEVE explosion.

3. IF the valve is taken out through a wall and/or to a location not readily visible by building occupants, in order to know if the valve is leaking (and thus that a dangerous condition exists) install a Tundish fitting (Search InspectApedia for "tundish" to read details).

Question: handyman did wierd repairs on water heater leaving the heater bottom askew with insulation oozing out

(Jan 13, 2016) Jennie said:

Hi I just sent you an email with further pictures and info. Electric water heater in our rental, the bottom left of the rim has raised 1/4". Glue/insulation from inside is showing. I'd like to test the valve but a plumber was here in October and said it worked. Yesterday they sent a handyman when I complained of the "shift", he's says it's okay. What do I do?


I can't guess at what's going on from this e-text and wait your photos. If the heater was modified it might be unsafe.

Question: Can a handheld shower head, with shut off valve, cause temperature release valve on water heater to open?

(Mar 1, 2016) David said:

Can a handheld shower head, with shut off valve, cause temperature release valve on water heater to open? I have a leaking temperature release valve and I think it's due to when we shut off the shower head, to save water, the pressure in the lines is getting pushed to the water heater and the release valve is opening. Is this possible, and if so, how to fix? We would like to continue to use the shower head. Install a expansion tank?

Reply: no but other conditions can cause TPR valve leaks: that's unsafe


In my OPINION, probably not. Though water hammer (that can be caused by some plumbing controls, valves, faucets) can cause the TPR valve to open, leak, or drip. And a combination of water hammer and high building water pressure increases that leak risk.

Search for WATER HAMMER NOISE for details.

(Mar 5, 2016) David said:
... thanks for your input on my situation with our water heater TPR valve. My wife and I have never heard the water hammer noise when we've closed the shower head. We hear a hissing sound, thought it was pressure having a way to escape. We've recently bought this house and the water heater is approximately 5 years old.

The TPR valve looks like it was replaced at the same time, being with the research that I've already done, the TPR valve should be replaced with the new water heater. The only other information I could provide is that I did turn down the water heater temperature, again to save money. Both thermostats are set at 125 degrees. In your opinion, what could be causing the TPR valve to open? Could the valve already be worn out, faulty, or should I have someone come and look at it and see if its just the layout of my plumbing?

Causes of leaks at a water heater TPR valve are discussed at

Reply: hissing at the shower head?


Where are you hearing the hissing. If it is right at the water heater that may be normal; Particularly some electric water heaters will hiss as the element is heating up incoming cold water, or scale in the heater may cause hissing as well as rumbling or other noises in the heater as it heats water.

There should be no discharge from the TP relief valve. If there is a discharge of water (or rarely, air) then either the valve is bad or the system is at an unsafe temperature or pressure.

Compare the rating of your TPR valve to the set temp of your heater; you could perhaps also measure water pressure there, attaching a portable pressure gauge to the heater drain valve. ( )

If you are hearing hissing at the shower head after turning water off at that fixture, that's a new one on me and I'll have to do some research.

(Mar 10, 2016) David said:
... thanks for your input. To elaborate on the hissing sound; that sound comes out of our shower head while the shower is running (showering). We control the water pressure coming out of our shower head by the shower shut off valve.

My water heater thermostats are set at 125 degrees, so I have a tendency to this it's pressure. Thought: When we moved into this house we, my Wife and I, went to use the sink in the kitchen and I had to turn the cold shut off valve down a little, not all the way, to control the amount of water pressure coming out of the faucet; just like we do with our shower. With the cold water shut off valve completely open, water comes out with a lot of force. Could this be a clue to the TPR? That the water pressure coming from the main line coming into the house is too high? Isn't there a pressure control valve/monitor on the main line coming into the house?

If this is most probable to answer the TPR valve problem, do I need to have the pressure control valve/monitor looked at, or install an expansion tank?

Reply: check building water pressure

Indeed shower head noise is related to pressure and flow rate through the device. Some shower heads mix air or use other flow restricting designs to reduce water usage while giving a strong spray. I'd try changing the shower head to see if the noise changes.

I doubt the shower head noise is related to temperature.

Start by checking the building water pressure and pressure regulator device(s). If your pressure is over about 70 psi that's a bit high and not just noise but leaks can be an issue.

Surely hissing at the shower head is independent from hissing noises at the water heater.

Reader follow-up: excessive building water pressure caused TPR leaks

2016/03/27 David said:
... thanks again for all your help. After I replied to you last time (anonymous).

I was doing research on water pressure gauges, completely coincidental that, that was your suggestion, and during one of the videos the instructor stated that your TPR valve will leak if your water pressure is too high. So I went to Lowes bought me a water pressure gauge.

And what did I read...110 PSI. Did a functions test on my water pressure reducing valve and noted no difference. Replacement of the water reducing valve will hopefully fix the problem. Thought you would like an update. Thanks again for your help.



Indeed 110 psi input water pressure at a residential building is too high. Pressures over 70 psi invite plumbing leaks at various fixtures.


we discuss the thermal expansion of water - pressure increases a bit as we heat up water in a closed system. (That's why some hot water systems include an expansion tank). "Typically the pressure/temperature relief valves on domestic water heaters are set to open at 100, 125, or 150 psi (6.9, 8.61, or 10.34 bar)."

So with a starting pressure of 110 psi, it'd be not a surprise if the water heater TPR was leaking. Take a look at the label on your TPR valve on your water heater and let me know the brand, model, and its operating pressure and temperature range.

And yeah, if you cannot successfully lower the incoming water pressure to say 70 psi, I'd replace the pressure regulator OR - at some buildings it's necessary to install two stages of water pressure regulators to handle very high incoming pressure.


Question: whenever the hot water gets turned on, there is a intermittent bang sound

Will said:
My water heater was got replaced 6 months ago. Since then whenever the hot water gets turned on, there is a intermittent band sound occurs. It only happens when hot water turns on.
Just wondering if this is related to the pressure valve. Any idea?


Will, please search for WATER HAMMER NOISE DIAGNOSE & CURE to read the probable cause as well as solution to this problem. Watch out: banging pipes due to water hammer can also cause the water heater's temperature/pressure relief valve to discharge or leak. Over time that could become unsafe.

Question: blow off valve on hot water heater is required to be six inches from the floor?

(July 20, 2016) MFA said:
Village inspector for pending home purchase said "blow off valve on hot water heater is required to be six inxhes from the floor." But arent these valves pre-installed into the heater? How can I raise or lower it???

Reply: no, not the valve, the opening of the valve's discharge pipe

No, the valve, properly called a temperature/pressure relief valve, is installed in a tapping on the water heater tank, typically near or on the tank top where water is hottest.

But yes, the TPR valve must have a discharge tube that terminates close to the floor or at an approved location to reduce risk of scalding someone if the valve opens.

Question: testing the relief valve blew off a washer

(Sept 1, 2016) davidmichaelborthwick said:

I did this WATER HEATER TPR VALVE TEST and out popped a little red washer thing split in half? can i replace it? or do i need a new valve?


David, if the washer was an internal part in the TP valve, while the part might be replaceable (some valves can be disassembled) I'd just replace the whole valve. It's a safer course. I once made an emergency midnight repair by cutting a new washer out of a piece of tupperware - so that the house could have heat until the next day when we could pick up a replacement valve. But nobody would be willing to bet the lives of building occupants on a modified relief valve. We put in a new valve the next morning.

Question: tankless water heater randomly shoots out water like a hose

(Sept 8, 2016) Marcy K said:
My tankless water heater randomly shoots out water like a hose would the TMP valve was replaced-plumber is saying pressure from the street is too high and we should install a PRV to control water pressure and resolve issue-Could there be any other issues? is this common and the common fix?


Yes. In addition to excessive water pressure or unsafe water temperature, water hammer can cause relief valve discharge or leaks.


Question: shouldn't water temperature also be adjusted

(Sept 8, 2016) Marcy K said:
also from reading the thread if the plumber is only installing a PRV and not adjusting heat then isnt that unsafe and not proper? Its my understanding heat & pressure have to be adjusted?


If street pressure is too high the TPR valve will indeed be likely to spill water as it heats up; this is an unsafe situation for several reasons, risking at the very worst blowing up the system if the repeatedly-spilling valve becomes clogged.

Check the incoming water pressure and compare that with the pressure range your heater manufacturer says they can handle as well as comparing it with the operating pressure of the TPR valve. You may need to install a pressure regulator at the point at which water enters the home. THat's a common repair.

Also see ANTI SCALD VALVES / MIXING VALVES for protection against burns from water that's too hot

Question: should the heating boiler or water heater temperature gauge also be adjusted when we adjust water pressure?

(Sept 8, 2016) Anonymous said:
If the pressure is adjusted does the heat/temperature gauge also need to be adjusted?


No. The gauge should be reading the actual system conditions.

Question: can you drain the water heater to remove scale through the relief valve?

(Sept 15, 2016) Gary said:

I have a gas water heater pressure/temperature valve that needs to be replaced. Have you ever drained the water inside the water heater through the pressure/temperature relief valve as far as possible, then remove the valve for a quick change with a new one. I expect some water to run out during the valve replacement.

The water heater is about 17 years old, and probably never had a maintenance draining all that time.

The water heater has a bottom plastic drain valve, and I would rather not go there to drain the water down, knowing the calcium deposits in the bottom could get stir up causing added problems, not to mention the plugging up of that bottom drain valve, possibly getting into the hot water piping running to the sink faucets on startup.

Reply: no

Gary the TPR valve will only drain off the water down to the valve mounting tapping; That's close to enough though you can expect a bit of spillage when you remove the old valve. Also search for WATER HEATER DE-SCALE as that operation is in your future - scale removal.

Question: leaks at the TP valve mount

(Sept 29, 2016) Mike said:
Water smears out of the water tank body where TP valve is connected. What should I do?


I think you meant water leaks out, right Mike? It may be possible to repair this leak - IF the tapping into which the relief valve is screwed is not badly corroded. You'd need to drain the tank below the level of the tapping, remove the valve, clean the treads, and using pipe dope or teflon tape, re-make the connection using a new TPR valve (to be safest).

Question: leaks at the relief valve when we take a shower

(Oct 3, 2016) richard said:
when we take a shower the hot water drips out of the pressure relief. what is the problem is the temp set to high?


I would look for a problem with temperature set too high, thermal expansion, or water hammer.




Question: increase water pressure at the boiler to get more heat in my home?

(Oct 26, 2016) Michael said:
I want to increase water pressure from my boiler to get heat to more baseboard heaters. The boiler recommends 30 lbs relief valve. Should I change it to 45 lb


Nope. You'll make your boiler unsafe. See BLEVE EXPLOSIONS

Don't try it. Instead check with your heating service tech to review the boiler's temperature settings on its aquastat. Search InspectApedia for AQUASTAT SETTINGS to read details.

Question: water heater relief valve discharges through a wall

(Nov 14, 2016) Bill said:
My existing gas hot water heater has the t&p valve on the top of the tank and it ties into a pipe that discharges through a wall to the outside.

My question is my new water heater has a side mounted t&p line that is located on the side of the tank and on the opposite side of where the piping stubs out of the wall for discharge. What do I do in this situation?


Watch out: never pipe a relief valve discharge tube "up" from the relief valve - doing so risks BLEVE EXPLOSIONS from a clogged valve. You'll need to make a new side wall discharge to a location that is always visible.

Question: TPR valve leaked when the water heater was replaced

(Dec 5, 2016) Scott said:

I just replaced my water heater (electric) and it is was very cold in the attic about 44 degrees. Water fill was very cold as well. No leaks at fill up and run to get air out of the tank / lines.

Applied the electric and in a few minutes as the tank heated I got some leaks through the T&P valve. I opened and closed the valve a couple of times. After about 30 to 45 minutes it no longer seems to be leaking. Is this normal on a brand new water heater?


Not normal, no, that is, as long as your building water pressure was at normal limits. Perhaps the valve was not properly seated. For safety I'd prefer to replace the valve as I'm not sure what it might do in the future. But first see THERMAL EXPANSION TPR VALVE LEAKS

Question: are relief valve leaks ever normal?

(Dec 14, 2016) Heater said:
Water incoming supply turn on during test. Pressure relief valve open manually. Water drip from pressure relief valve. Is it normal?

Reply: no

no, Heater, it is not normal for the pressure relief valve to be leaking. And it is unsafe because eventually the leak can lead to a clogged valve which then could lead to an exploded heater. However it is normal for a little water to drip out of the discharge tube for a moment or two after testing.

Question: Is the relief valve suppose to be horizontal or vertical

2017/01/01 Anonymous said:
Is the relief valve suppose to be horizontal or vertical


The relief valve discharge opening or "mouth" must point DOWN

Question: I don't see why hot water expansion would ever cause leaks

2017/01/08 GaryC said:

You go through alot of effort to explain how heated water expands and the resulting increase in pressure. All that is well and good for theory. In a domestic (North American) water supply system, to the best of my knowlege there is nothing to prevent the expanding water/pressure from the hot water heater from just backing up into the supply plumbing and hence the water pressure in the hot water heater would NEVER exceed the supply pressure. Or is there a required one way valve somewhere in the system I am not aware of say in the hot water heater?


Please see this question along with a detailed reply now found at THERMAL EXPANSION TPR VALVE LEAKS


Continue reading at RELIEF VALVE LEAKS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.





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