Gradually increasing water pressure

[troutandcarp]

Hi,

I'm having water pressure in my home that gradually builds up. The water comes from the city. Right after my main inlet valve I've got a prv. I thought the old prv was the problem initially, so I bought a new one from home depot and replaced the old one. The problem seemed fixed for a day but has returned after sitting last night. The pressure is set at 50 or so psi on the prv, but it goes up into the 90s and higher during the night. After opening a faucet in the house, the pressure will go back down to around 50, but once closed, then it immediately starts gradually increasing at around 10 psi every thirty seconds. After using the water in the morning for a half hour or so, the pressure seems to sit steadily at around 50 . But it seems after the night, the problem returns. Could the new pvr be bad, or is there some other possible problem? I'm at a loss.

 

[johnjh2o]

Sounds like it's a thermo expansion tank problem. If you have one it may need to be replaced, if you don't, one needs to be installed.

 

[ExtraMilePlumbing]

Sounds like it's a thermo expansion tank problem. If you have one it may need to be replaced, if you don't, one needs to be installed.

How is the thermo expansion tank the cause of this problem.please explain thank you very much.

 

[johnjh2o]

The PRV acts like a check valve not allowing the increased pressure (due to the water heater) to dissipate into the City water system. Causing the pressure to increase in the home.

 

[Mr_David]

This is how I would explain it. Water does not compress like air when you heat it. In a closed system, when water is heated it expands and creates pressure.
The basis of steam powered engines.
Try turning off your water heater for a bit and see if the pressure rises. If not then problem is thermal expansion from the Water heater. An expansion tank has an air bladder inside that that will compress when the water expands therefore reducing the increase in pressure.

PRV's often have a bypass that does allow thermal expansion to flow back into the main but only if that pressure exceeds the main pressure. 90 psi can't push back into a 120psi system.

The ones I use have a by-pass Wilken/Zurn600XL


Also even a new PRV can leak by. Debris on the seat.

 

[troutandcarp]

Thanks for the info! It looks like the problem is probably that I need an expansion tank. The pressure seems to be going up in relation to the heating from the hot water heater. There isn't any expansion tank on the system at the moment.
When installing an expansion tank, it goes on the cold line running into the heater, correct? Is it better to place it as close to the heater as possible, or does the distance from the heater not make much difference?
Thanks again for all the info!