My house is in the hills; the water coming in from the city is 170psi. I have a Wilkins 600XL regulator that was installed about 10 years ago. Over the last year or so we have been getting high-pressure surges when a faucet is opened in the house. This lasts a few seconds and then calms down. I checked the pressure in a hose bib that comes off the regulator (about 20 feet away) with a Watts Test Gauge (with the twin needles) and it showed 120psi when placed on the bib (after releasing some water first). The red needle, though, capped out overnight at 160psi.
I bought the repair kit for the 600XL and installed all the new parts (all the old parts were very deteriorated). The pressure then read as 60psi but I was still getting faucet surges. The overnight reading was back at 160psi. I cranked down the regulator and now the “regular” reading is 40psi (and the pressure coming from the faucets seems pretty low), but we are still getting faucet surges and the overnight was again in the 160psi range.
I just purchased a Watts PLT-5 thermal expansion tank (there was not one on the system) but have not installed it yet because the PLT-5 is rated for 150psi max--and is supposed to be set to match my regulator’s 60psi output). I am concerned about the tank catastrophically failing if the overnight pressure hits 160+psi (as it has been doing).
So I thought I'd verify that the water heater is actually causing the pressure build-up when the water heats. I turned off the water heater last night (and ran the hot water in the house out until is was lukewarm). The gauge says the overnight pressure was 160in again, while the regular reading is 40psi.
There is a hose bib (for the garden) near the regulator that is not regulated, and that one reads consistently at 170psi.
Any thoughts on what might be causing these issues? Is there a possibility that the unregulated pipes for irrigation might be somehow mixing into the regulated pipes? What else can I do to get the overnight pressure down? Thank you for any help!