Water heater safety valve diagnosis:

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

This article series explains the requirement for temperature and pressure relief valves on water heaters, calorifers, geyers, or hot water cylinders, and we give relief valve installation, inspection, diagnosis and repair procedures for these important safety devices.

Temperature & Pressure Relief Valve Questions & Answers

These questions and answers about TPR valves or temperature/pressure relief valves on water heaters were posted originally at RELIEF VALVE, WATER HEATER - be sure to review the diagnosis and repair advice given there.

Some of the FAQs discussed below have been adapted from information provided by the Watts Regulator Company in "52 Questions and their Answers", Watts Regulator Corporation (1973) cited in detail in ther eferences of the original article link we gave above.

On 2020-11-15 - by (mod) -

Levi:

Sorry I don't get the question.

The TPR valve selected depends on the type of heating appliance and its fuel and thus the operating temperature range and pressure range.

Across water heaters, the relief valve will normally

- open at 150 psi pressure
and/or
- open at 210 degF temperature

and must be capable of discharging energy (as BTUs) at a rate greater than the input rate of the water heater's energy source

To simplify life you'll typically find TPR valves sold in BTU capacity ranges

1 group for heaters rated at Under 200,000 BTU Per Hour Input Rating

a second group for heaters rated at Over 200,000 BTU Per Hour Input Rating

You can easily verify the TPR valve on your 40 gallon water heater by looking at the information on the relief valve data tag and comparing that with the INPUT BTUH rating of your water heater.

See details at

WATER HEATER TPR VALVE SIZE https://inspectapedia.com/plumbing/Water-Heater-Relief-Valve-Repair.php#TPSize

On 2020-11-11 by levi

what is the difference? and what is commonly used on a 40 gallon water heater?

On 2020-10-25 - by (mod) -

Lyt

At RELIEF VALVE LEAKS

https://inspectapedia.com/plumbing/TP_Valve_Leaks.php

We give the causes and cures for leaks such as you describe. Take care of the door important safety concerns here and be sure to read that article

On 2020-10-24 by Lyttle combs

My water heater is leaking water from temp. And pressure valve and how do I fix it.

On 2020-06-25 - by (mod) -

If water pressure is high the expansion tank may be too small,
Or
There may be another cause such as water hammer or wrong TPR valve

On 2020-06-23 by Richard Stafford

Great info here, but I have an ongoing problem. On a fairly new electric hot water heater tank (2 years) I replaced the relief valve because it was leaking and occasionally discharging. However the new relief valve did not correct the problem, still leaks constantly. So, I replaced both thermostats thinking one or the other was not shutting off the heating elements and it was over heating and discharging. Still, it drips out the relief line.

There is a new expansion tank on cold line.
I could replace heating elements but I do not think that is the problem.

After reading here it seems maybe it is a water pressure problem. But I would have thought the expansion tank would have solved that.
Any ideas?
Richard Stafford

On 2020-05-23 - by (mod) -

Vanessa

In the Related Articles list above, please see the diagnostics in

RELIEF VALVE LEAKS

If your incoming water pressure is a bit high, or if there is a water hammer oroblem you may need an expansion tank, else the valve may need replacement.

On 2020-05-23 by Vanessa

I think it is called TRV it is the valve on the overflow pipe.

@Vanessa,
Also the water heater is only 2 yrs old. So not an old machine.

Water heater overflow pipe constantly dripping so I tested the TRV and water gushed out of pipe like I turned on a faucet. So I let go of it. I know that is not normal.

The pipe is hot so I checked my heat settings and turned it to 120 degrees ) it was a little above that ) It is still constantly dripping (trickle not drip drop). Suggestions?

On 2020-02-13 - by (mod) -

Sallu

Step through the diagnostics at RELIEF VA LOOK VE LEAK CAUSES https://inspectapedia.com/plumbing/TP_Valve_Leaks.php

And let me know what you find.

On 2020-02-13 by Sallu

Dear Sir,
I have problem of my apartment have 2 Ariston 40ltr water heater.but I got problem my only one water heater pressure relief valve water dripping.my plumber change 2times of pressure relief valve but still same problem when I on my water heater it's dropping after few minutes. How I solve this problem?

On 2020-02-04 0 by (mod) - difference in a long stem and a short stem on a hot water heater pop off value?

Eddie

On some water heaters the shorter stem is needed because given the TPR valve mounting position, such as a side-mount TPR valve, the long stem might touch an internal part of the heater such as a center flue or a dip tube.

On 2020-01-31 by Eddie

What is the difference in a long stem and a short stem on a hot water heater pop off value?

On 2020-01-11 by (mod) - expansion of water or increase of water pressure in a water heater.

Tom,

Thanks for asking an important and interesting question on the expansion of water or increase of water pressure in a water heater.

The pressure in a closed tank of water will indeed increase as the water temperature is increased.

Your water heater pressure of 140 psi may be quite normal. The actual pressure increase will depend on

- the temperature of the incoming water

- the temperature to which the water is heated

- and an effect of the thermal expansion of water as it is heated

When the water heater (or in other countries cylinder or calorifer or geyser) is cold the pressure inside it should be the same as incoming building water pressure - in your case 70 psi.

At the article we cite below we note, as do water heater manufacturers, that
"For each 10°F increase in temperature, water expands 0.2% "
So if your incoming water were cold, say 40 degF, and you heat it to 140 degF, the volume of water will increase by 2%.

If the expanding water were in an "open" system that expansion would just push back into the cold water pipes and pressure wouldn't increase. But where there are check valves or other obstructions in the piping system, pressure can build rapidly as water is heated.

A domestic water heater is typically designed for up to 150 psi working pressure. At higher pressures we expect the temperature/pressure relief valve to open to relieve pressure.

But in some homes the water heater pressure just from thermal expansion causes dripping at the TPR valve (an unsafe condition); in that case, if all else is normal, yes it makes sense to add a thermal expansion tank to the water heating system.

SeeHOT WATER EXPANSION TANKS

Also see THERMAL EXPANSION of HOT WATER for further explanation of the actual amount of expansion that occurs in heated water.

On 2020-01-11 by Tom

If my residential pressure is 70 psi which of the pressure inside my hot water heater tank be? It’s fluctuating from 140 psi to as low as 45. I think the expansion tank is my next replacement of course. But what should the pressure in the tank normally be in relation to the system pressure?

On 2019-11-23 by (mod) - water coming out of a pvc pipe that is located coming out of the house.

I'm just your text I really don't have an intelligent guess about why the pressure or temperature relief valve is discharging but it's definitely a safety concern.

How do I make the heater itself be unsafe now, but even if the problem we're simply a leaky valve itself that leak can lead to clogging which in turn can cause the valve to fail to open in an emergency. The result of that would be a dangerous explosion of a water heater

On 2019-11-22 by Thomas Napier

I just happen to notice water coming out of a pvc pipe that is located coming out of the house. Our hot water heater is located on the 2nd floor and have come to the conclusion that the TPR valve engaged itself. I understand that this works because either the temp. or the press. became too much and this is the safety feature at work.

My question is, why now? We haven't increased the temp. of the water, and its not what I would consider cold outside, let alone, this is upstairs in a climate controlled area. Is this an indication that something is wrong, or is it possible the last time I increased the temp. on the water heater, it has been discharging all this time and I just never was outside when it did it?

On 2019-09-17 by (mod) - Why do We have a huge water bill.

Sarah

Watch out: What you describe is improper water heater operation and is extremely dangerous, risking a catastrophic BLEVE EXPLOSION. inspectapedia.com/plumbing/BLEVE-Explosions.php

When a water heater is overheating the increase in pressure or temperature or both cause spillage of water at the temperature and pressure relief valve. The purpose of the relief valve, also called TPR valve (temperature, pressure relief) is specifically to prevent over-pressure from bursting or exploding the water heater tank. Working properly, then, the TPR valve is a critical safety device.

When that condition (overheating, TPR spilling) is permitted to continue for some time, deposits of minerals, silt, debris from the hot water moving through the TPR valve mouth, can ultimately clog the relief valve.

If a relief valve clogs it can fail to open in response to over-temperature or over-pressure. The result can be an exploding water tank with great force and damage and risk of injury or worse.

If the heater has not been properly repaired already, it should be turned OFF IMMEDIATELY and you should have the heater or its controls repaired by a qualfied plumber.

I don't understand your phrase "The realestate is giving us a hard time", but I warn that whoever that is, the are risking severe building damage and personal injury to anyone who may be in or even near the building where the conditions you describe exist.

Please clarify and keep me posted.

On 2019-09-17 y Sarah Lagasse

We have a huge water bill. We had plumber our who found no leaks with the water heater but did find it was massively over heating which meant the tempature gage was broken.

He said that when the water get to hot it releases I assume through the TRV. This would be the cause of excess water as it would then refill.
Just wondering if anyone can confirm and give me some tech details. The realestate is giving us a hard time.

On 2019-05-28 by (mod) - where is the T&P valve supposed to be installed

On most water heaters the tapping for hot, cold, dip tube and relief valve are marked by a label or a stamping into the steel. If you don't see that we need to start with the manual which means you need the brand and model

Watch out: do not install a T&P valve at a more-remote spot like downstream on the hot water piping, and do not modify the relief valve in any way - doing so is unsafe.

On 2019-05-23 by dave

my new water heater came without a t and p valve. does it get installed on top or side of heater? the side hole is plugged and the top hole is open.

On 2018-12-29 by (mod) - now we have no hot water

Anon:

IF you water heater is electric

AND the water level in the heater dropped below the electric heating element

AND the heater was turned on

THEN the element may have burned up.

Try first turning the system off and back on

Try also checking for a tripped button on the temperature limit control

Then use the on page search box to find our article entitled

How to Test for a Bad Electric Water Heater Heating Element

let me know how that works for you.

On 2018-12-29 by Anonymous

Someone opened the pressure valve by accident and water heater went into vacation mode and now we don’t have hit water

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.

Reply:

John I don't understand the 'worn seat" in a temperature/pressure relief valve - but then I'm not on the scene.

A temperature/pressure relief valve does not normally open nor cycle open and shut frequently, 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.

Check first that the water heater is operating at a normal temperature and pressure and that you don't have a water hammer problem.

Then see these diagnostic articles

• THERMAL EXPANSION TPR VALVE LEAKS
  
  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.
• RELIEF VALVE LEAKS - all causes of TPRV leaks

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.

Reply:

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.

See BLEVE EXPLOSIONS

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.

Reply:

Jane,

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?

Reply:

Noel,

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 InspectApedia.com 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?

Reply:

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.

Reply:

K Y

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

See inspectapedia.com/plumbing/Hot_Water_Expansion_Tanks.php 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?

Reply:

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.

A TYPICAL water heater TPR valve will open at

• Temperature Relief: 210°F (99°C),
• Pressure Relief Range: 75 to 150 psi (5.2 to 10.3 bar)

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

Reply:

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.

Anon

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 horribly....is it possible that all that monkeying around the first time ruined a brand new valve?

Reply:

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.

See WATER HAMMER NOISE DIAGNOSE & CURE

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?

Reply:

Juanita

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.

See RELIEF VALVE LEAKS

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

Reply:

Kevin,

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.

See RELIEF VALVE DISCHARGE TUBE

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

Reply:

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?

Reply:

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.

See details at RELIEF VALVE DISCHARGE TUBE

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?

Reply:

Jayant

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.

Reply:

Dave,

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.

Reply:

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

ELECTRIC WATER HEATER ELEMENT TESTSinspectapedia.com/plumbing/Electric_Water_Heater_Element_Test.php

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.

See WATER HAMMER NOISE DIAGNOSE & CURE inspectapedia.com/plumbing/Water_Hammer_Noise.php

and see WATER PRESSURE MEASUREMENT inspectapedia.com/water/Water_Pressure_Measure.php

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.

Reply:

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

ELECTRIC WATER HEATER ELEMENT TESTS inspectapedia.com/plumbing/Electric_Water_Heater_Element_Test.php

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.

See WATER HAMMER NOISE DIAGNOSE & CURE inspectapedia.com/plumbing/Water_Hammer.htm

and see WATER PRESSURE MEASUREMENT inspectapedia.com/water/Water_Pressure_Measure.php

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

Reply:

Glenn,

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?

Reply:

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

David

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 InspectAPedia.com 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

• RELIEF VALVE LEAKS - all types of TPR valves
• RELIEF VALVE LEAK FAQs - - diagnostic questions & answers about all types of TPRs & TPR valve leaks
• RELIEF VALVE, WATER HEATER - TPR valves on water heaters
• RELIEF VALVE, WATER HEATER DIAGNOSTIC FAQs - diagnostic questions & answers about water heater TPRs & TPR valve leaks on water heaters

Reply: hissing at the shower head?

David

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. ( inspectapedia.com/water/Water_Pressure_Measure.php )

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.

Reply:

David,

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

At inspectapedia.com/plumbing/Hot_Water_Expansion.php

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.

Details are at WATER PRESSURE REDUCER / REGULATOR

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?

Reply:

Will, please search InspectApedia.com

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?

Reply:

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?

Reply:

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

See WATER HAMMER NOISE DIAGNOSE & CURE

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?

Reply:

Marcy:
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 & TEMPERATURE CONTROL / 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?

Reply:

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 InspectApedia.com 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?

Reply:

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?

Reply:

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

See THERMAL EXPANSION TPR VALVE LEAKS

See WATER HAMMER NOISE DIAGNOSE & CURE

See WATER HEATER TEMPERATURE TOO COLD or TOO HOT

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

Reply:

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?

Reply:

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?

Reply:

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

Reply:

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?

Reply:

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

...

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

Or see RELIEF VALVE, WATER HEATER DIAGNOSTIC FAQs-2 - more-recent questions and answers about leaks at water heater or calorifier relief valves

Or see these

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