I have high water pressure coming into my house (~110psi) and a backflow preventer at the source. I do not currently have a pressure regulator or an expansion tank installed, though I'm considering doing this.
Currently my T&P valve is leaking via a slow drip (maybe 3-4 cups/day). I've taken a reading of the pressure and if I'm not using the hot water (i.e., overnight), the pressure gradually increases to 150psi when the T&P valve releases. My understanding is that as the water heater heats water in the house, pressure increases and has nowhere to go because of the backflow preventer. The T&P valve releases at 150psi, which is why my pressure spikes to this level overnight or when I'm not using the hot water.
I have purchased an expansion tank and a water pressure regulator, and plan to install them. My question:
Will the water pressure regulator prevent the pressure from increasing over ~50-70psi (or whatever I set it to) during times that I'm not using water? If not, how can I prevent my hot water heater from leaking at the T&P valve during periods that I'm not home?
My fear is that because the system is closed the water heater will slowly build up pressure until the air bladder in the expansion tank reaches 150psi, and then the T&P valve will leak anyway. Perhaps it would increase the time before the leak begins, but if I leave for any period of time the leak will recur.