Hot water heater leaks from the t & p relief valve

[Kmason]

Hi, I have an Indirect hot water heater that lets water by the relief valve. I have replaced the T&P relief valve and still get water leaking by. I noticed that when I ran the hot water enough for the boiler to kick on the relief pipe stayed dry untill the temperature of the boiler read about 175 psi.

 

[Beni]

I assume the 175 was degrees F and not psi. If its 175 degrees F are you using the boiler for space heating too. If the new relief valve was the standard water heater relief valve it probably will start dripping at 175 degrees. If you need 180 degrees for space heating, your going to need to get a relief valve with a 190 degree F temp setting. If the boiler only serves the water heater, turn the temperature setting on the boiler down to 140 degrees max.

One other thing it could be is if the expansion tank is water logged. That would cause the T&P to leak too.

If it's 175 PSI then stop turn everything off and call a plumber quick.

 

[AQualityPlumber]

If this problem persists after switching tnp then make sure that the expansion tank is on the hot outlet side and not defective. If your tank has heat trap nipples it will prevent hot water from expanding into the cold feed during recovery. If this is the case and your expansion tank is on the cold inlet side, the thermal expansion will cause the tnp to leak just a little when recovering. I have ran into this more then once.

 

[Kmason]

I read on another site about two possible causes for a leaking T&P relief valve. One was having high water pressure and I have a booster pump installed inline on the cold main supply. So I disconnected the pump and it seems to have resolved the issue. Thanks everyone for your help.

 

[Caduceus]

If the booster pump was needed and there was no issue before, you should still consider what AQuality and Beni have suggested. Removing the booster pump may only be relieving the symptoms, but the true problem still remains.

 

[johnjh2o]

I'm sure your booster pump has a check valve on it. That check valve is what requires you to have thermo expansion tank. Without the tank when the water heats it will expand, causing the pressure to go higher then the T&P valve is rated for.

John