Chris Bryant wrote:
The water heater acts as an accumulator in the system, whether you run the hot water or not. It is working the way it is supposed to- if there were no air cushion, the system pressure would rise enough to trip the PTR valve on the water heater every time you heated water.
This is correct.
If you misset the winterizing valves for the water heater, it may be possible (depending on your setup) to have its entire volume act as an accumulator. That can lead to very strange behavior: having water pressure for a good long time after turning off the pump or city water connection, having the pump seemingly never shut off, etc. Don't ask me how I know this....
