minor leak at hot water tank T&P valve

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qmqmqm

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Hi everyone.

Here is what happened at a townhouse:
A T&P valve leaks on an older hot water tank.
Replaced it with a new tank. Still leaks.
Changed the T&P valve on the new tank. Still leaks.
The leak is very slow - about a litre per week.
Turned down the valve a bit at the tank's cold water supply. It leaks less.

I'm not certain if the leak is constant or only happens sometimes.

City water pressure is normal. The tank is not over-heated. There is no pressure regulating device at the house.

What could be the problem, and the recommended solution?

Thanks!

Paul
 
How did you verify that your city water pressure is normal? Many times, the Pressure Reducing Valve will go out and will push 100PSI or greater down to your water heater, causing the T&P to fail. Also, I've been taught to never flip the valve open since it will push crud from the water heater and stop the seal from sealing. Go spend $13 and get a hose bib tester and verify your water pressure.

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By the way, we have dozens of professional plumbers at our sister site called:

www.plumbingforums.com

who are there to answer any technical plumbing issues you may have.
 
Did you happen to install the necessary expansion tank when you replaced the hot water tank?
Seems like this would solve your problem.
 
Thanks for your responses!

Havasu, a technician measured the water pressure to be 50 psi. This matches the Pressure Reducing Valve (PRV) on the main line. The PRV's label also reads "50 psi".
 
The Hot Water Tank's manual says if there is a Check Valve at its cold water supply, an expansion tank is required.

I have this valve at the cold water supply. Is it a check valve? Does the arrow mean it is a check valve?

1.jpg2.png
 
Thanks for your responses!

Havasu, a technician measured the water pressure to be 50 psi. This matches the Pressure Reducing Valve (PRV) on the main line. The PRV's label also reads "50 psi".

@havasu You are right! The same company came back and tested the water pressure again, this time from the faucet in the garage. That faucet is very close to where the city water comes into the house, and does not have any bypass mechanism to reduce the pressure. This time, the pressure fluctuated a lot. It turns out that the Pressure Reducing Valve was the issue. After replacing it, the leak from the T&P valve has stopped. Thank you!
 
Did you happen to install the necessary expansion tank when you replaced the hot water tank?
Seems like this would solve your problem.
Thanks for your advice, user 4883!
The technicians on site also recommended expansion tanks.
There has been no issue after the Pressure Reducing Valve (PRV) was replaced. And the house never had an expansion tank since it was built 15 years ago. So I guess I can do without it...
 
The Hot Water Tank's manual says if there is a Check Valve at its cold water supply, an expansion tank is required.

I have this valve at the cold water supply. Is it a check valve? Does the arrow mean it is a check valve?

View attachment 30818View attachment 30819

From here, it looks like an older Caleffi EA type "Anti Pollution Valve". (European name for a check valve.) Yours may be a different brand.
Paul
PS: The arrow indicates direction of flow.
 
Did you happen to install the necessary expansion tank when you replaced the hot water tank?
Seems like this would solve your problem.
I agree with B , if you have a check valve or closed water system water in the tank will expand 1/23 what that means for every 23 gallons of cold water after heating you will have 24 gallons.
 
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