I have a recently installed hot water heater that is leaking from the overflow often. It has input pressure of 90psi determined by pressure gauge on outside faucet that comes direct from house infeed through pressure relief valve.
The pressure taken at bottom of tank is 115psi. Plumber said my prv was bad and needed replacing. Have not done because I discovered the surge tank is installed on the hot water discharge rather than the incoming water side. Can this surge tank be the problem with overflow and pressure difference? Should it be changed?

Hi KengFrang

If you have an EXPANSION TANK (surge tank) and it has a little cap on the bottom of the unit unscrew the cap and there you'll find a shrader type of valve similar to a tire valve. Insert a screwdriver into the bottom of the shrader valve to release some air... if water comes out then the expansion tank is blown and will need to be replaced. If air comes out pop back and let us know.

Removing the tank is a bit tricky when it is filled with water so be careful as it will be much heavier than you think it will be. One trick is to depressurize the water line and then drill a hole in the top of the tank and then drill another hole in the bottom of the tank to empty the tank of water... then you can remove the tank without all the weight!

Back to you...

Mark

90 PSI is pretty high for a house pressure and 115 is very high. However, most PRV's are set 150 PGI and 210*F. I have seen Expansion tanks on both hot and cold. However,in the county where I live, Cherokee Cty, GA, they are always on the CW side.

Yeah, at 90 PSI as a baseline pressure reading you should definitely consider installing a pressure reducing valve (PRV). Here, excessively high pressure can lead to excess wear and tear on orings, washers and other types of seals in the plumbing system that can lead to premature failure of a valve or a braided supply tube or similar and lead to a flood condition... not something to take lightly.

If you install a PRV you want to reduce the pressure to the home to about 65 PSI to start and see what you think of that pressure. Here, there will be a reduction in the water pressure to the home, but there will not be a reduction in the volume of water supplied to the home so in most cases you'll barely notice a difference but your home will be safer, for sure.

Check the expansion tank to see if it is water logged... most likely it is.

House should not have over 55 psi of pressure. As mentioned above, if higher than 55 psi, install pressure regulator.

The higher water pressure inside the tank can be caused by very hot water temperature in combination with nipples on top of the water heater, that prevent hot water from being pushed into cold water side via thermal expansion

Do this: put gauge on water heater / hot water side. Read pressure. Go inside the house, turn hot water ON in tub for 10 minutes. Turn it OFF. Go back to your water heater and read the pressure gauge again. See if the pressure dropped

Let me know how you did

Milo