I just replaced my pressure reducing valve (pressure coming in to the house was 120 psi and the valve had failed). I have the new valve set to 55 psi but I am still getting surges of 120, 140, and one that maxed out the gauge (over 200 psi). Is there a way to stop these surges? Should I be worried about them? Can these surges damage my on-demand hot water heater, fixtures, appliances, etc.?

What do you mean by "surges"? To me, a surge is a sudden pressure raise. Is that what's happening or is it a gradual pressure rise? Is there an expansion tank installed? Is street water pressure staying steady at 120psi?

No expansion tank. I have the pressure gauge on my washtub faucet. The gauge shows the current pressure and shows the maximum pressure experienced. I am assuming I am getting a surge from the street and that it isn't a slow building pressure as I have never seen the standing pressure over 60 psi. Is there some other reason I could be having these high pressures?

Forgot to note the house was built in 1984, copper throughout. Pretty standard plumbing system.

I just realized the on-demand heater. Is there a way to install the gauge on the street side of the regulator? Is there a relief valve on the water heater?



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We have an on-demand hot water heater. Do they cause the same thermal expansion issues as a traditional hot water heater?

Good call on checking the pre-regulator hose bib. I will move the gauge to see what the readings look like.

The relief valve on the water heater was one of the reasons I knew we had a pressure issue. There was a small puddle of water under the water heater at random times. There is no pattern to when the relief valve let's out some of the pressure (and water). This was one of the reasons I was thinking it was a surge from the street.

theoretically, since the on demand water heater only fires when a faucet is opened, there is no way excess pressure can be created.
i would still install an expansion tank. they are not expensive and install pretty easily.

An on demand water heater does not need an expansion tank. Someone would have to be there to do an examination to find out why the pressure is fluctuating. It should not be able to increase higher than the incoming city pressure.

Your heater may have been installed by someone who believes on demand heaters do not need relief valves. Some installations have a hose faucet ahead of the PRV, but not all.

IF you have a "functioning" relief valve, the pressure should NEVER rise above its 150 psi setting.

Installing an expansion tank, when one is not needed, will just "mask" the real problem by minimizing the symptoms.

So I moved the pressure gauge to the outdoor water spigot (which is before the pressure reducing valve in the basement) this morning and the max reading is 170 so far today. The standing pressure was 120 psi.

What's the maximum incoming pressure that the new regulator can handle?