Water Hammer recently in shower

[Tim Moyer]

I've noticed recently water hammering in our upstairs 1 handle moen posi-temp pressure balanced shower when water is being used elsewhere in the house. This is a new occurrence. The Moen cartridge is 15 years old. Would simply replacing the cartridge fix this issue?
I should also add that the hammer only occurs in one position on the shower handle. If it starts to hammer and can make it stop by making the water hotter or colder and slowly bringing it back to the starting position.

 

[Tuttles Revenge]

What you're describing sounds like a vibration or a chattering. My sister has a similar sounding effect in her Kohler pressure balance shower valve when the shower or other fixture is being used. In her case a thermostatic mixing valve was added to her water heater to bring a new 2 handle tub filler valve into compliance. My best guess would be that the pressure balance spool is cavitating(sp?) to try and compensate for a loss of pressure on one side of the supply (hot or cold) and as you make and adjustment to the valve manually, you are helping it to find that balance. Just a guess.

 

[Sponsor]

 

[WorthFlorida]

I had the exact problem after changing a Moen posi-temp with a Danco brand cartridge. Every time a faucet was turn off anywhere in the home you would hear a little knock from the shower faucet. I changed it to a Moen brand and the problem was fixed.

As described above it could be a vibration but everyone has a different opinion as what is water hammer.

Water hammer is a different kind of problem and I doubt you have a hammer problem. Just change the cartridge with a Moen brand. Inside there is a pressure balance valve (spool) that moves to prevent scalding Or cold water shock when the cold or hot water pressure drops. This little rod slides to close off either the hot or cold water flow slightly. This is what is making the knock noise. With a cartridge in your hand, shake it and you’ll hear rattling. That is the balancing valve.

 

[Tim Moyer]

Great! I have a new Moen cartridge ready to install. Thanks for the suggestion.

 

[Tim Moyer]

I had to purchase a cartridge puller to get the old cartridge out. I also found some rather "interesting "connections by the plumber that did the install a decade ago. There is a lot of movement around the valve body (the whole thing can be moved about 1" or more), maybe due to using PEX??? I'm not a plumber, so I don't know if this was installed correctly or if the valve body should be installed rigid with no movement behind the cover plate.
Anyway, the new 1222-B Moen cartridge had a slow drip after installation. Fortunately, I had a spare which took care of the drip after I installed it. So far, I don't hear any noise when other plumbing devices are used simultaneously.

 

[Tim Moyer]

I had the exact problem after changing a Moen posi-temp with a Danco brand cartridge. Every time a faucet was turn off anywhere in the home you would hear a little knock from the shower faucet. I changed it to a Moen brand and the problem was fixed.

As described above it could be a vibration but everyone has a different opinion as what is water hammer.

Water hammer is a different kind of problem and I doubt you have a hammer problem. Just change the cartridge with a Moen brand. Inside there is a pressure balance valve (spool) that moves to prevent scalding Or cold water shock when the cold or hot water pressure drops. This little rod slides to close off either the hot or cold water flow slightly. This is what is making the knock noise. With a cartridge in your hand, shake it and you’ll hear rattling. That is the balancing valve.

Interesting that with the old cartridge I can hear the rattling when I shake it, but not the new one. Maybe they've changed the design?