Mike H
New Member
Hello, hoping someone can help solve this problem. My house is 19 years old. Last summer my water heater failed and I had it and the expansion tank replaced. Six months later (December-ish) I started hearing a knocking sound in the walls when I flushed a toilet or turned on/off a faucet. I checked the expansion tank pressure and it was very high (off the scale of my tire pressure gauge). I then put a pressure gauge on one of my exterior hose bibs and found I had 140 psi. When I ran the water the pressure dropped down to 60 psi (where it should be) then when I shut the water off the pressure would creep back up 140 psi (within a minute or two). So I deduced I had a failed PRV and replaced it with a new one, with the same make/model as the original PRV. After this I still had the knocking sound in the pipes when turning on/off the water. I checked the expansion tank pressure again, and could not get a reading on it this time (tank failed). Called the water heater company and they swapped out the expansion tank (still under warranty). Now I have a new PRV and new expansion tank, but still have the knocking in the pipes. This weekend I did some more troubleshooting: Put the pressure gauge on the hose bib and ran my lawn sprinklers so I could observe the pressure gauge. I'm finding that every time the water shuts off, the water pressure instantly spikes up to 80 psi and then right back down to 60 psi, causing the knock in the pipes. I'm also noticing the my shower water pressure fluctuates when other faucets or water appliances are in use. At this point I'm thinking the new PRV valve I got was bad from the factory. Is there something else I might be missing? Thanks for any help.
