I had the same thing happen to me some time ago. The pressure rises because
it is a closed system, it cannot vent over-pressure to the street side of
PRV. The pressure rises because your water heater causes the water in your
heater to expand and create pressure. I solved it by using an expansion
pipe. Just a 3' long 4" riser of PVC pipe mounted anywhere in the system,
such as above an outdoor faucet. You can also buy expansion tanks (google)

--
Walter
www.rationality.net
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wrote in message
...
Hi, I have a mid-1980s house with an older pressure reducing valve
(PRV) from the street. I imagine it's at least 8 yrs old (owned for 8
yrs).

I have had 3 significant leaks in the place since I bought. First one
was in the slab, but the other two in the pipes between upstairs and
down.

The plumber who fixed the last one (recently) tested the water
pressure at the front hose bibb. When he turned on the water, the
meter said 50 PSI. We were both relieved that it wasn't something
unusual that would require yet another fix (the PRV). However, I
decided to buy a meter from Home Depot just to be sure and monitor on
a regular basis.

So I put on the meter, sure enough, it said about 50 PSI. Great. But
unfortunately, it started to build! After a few seconds it was at 90
psi. I think 90 PSI could contribute to pipes bursting, correct?

So my question:

Is the PSI at the time of just turning on the valve the one you read
or do you read it after the time that it stabilizes? I did adjust the
PRV down a bit but it would only go to just under 80 PSI. I think I
need a new PRV, correct?

I want to manage the water pressure to have minimal wear and tear on
the pipes.

Thanks for your help.

Matt