Possible reasons for shower to go all hot or all cold?

Question

I have a Moen shower trim that uses a 1222 cartridge. It seems that every year I end up with the situation that the water goes from all cold to all hot as I turn the handle. The changeover is preceded by a banging sound in the pipes as well as a decrease in water volume coming out of the shower head. (Turn from off at 6 o’clock position, rotate counter clockwise to about 11 o’clock position, bang!)

Once the water changes over to hot, if I slowly turn the handle back to off, it maintains all hot water while slowly decreasing water volume as I get to the off position.

The only way to get the cold water back is to quickly jerk the handle back and forth and watch for a water pressure drop and hear the pipes bang again, then water returns as all cold.

What are reasons for this issue happening? Do cartridges fail every year? I’ve probably changed this out at least 3 times now. Is my water supply that terrible? I am on municipal water.

Answer 1

Is this symptom only related to the shower valve?

Many thermostatic shower mixers have two back flow preventers (BFP) which should prevent these effects. A BFP could be also installed upstream of the cold domestic water inlet line of the heating system.

Some BFPs use a thin rubber-like diaphragm as a one-way mechanism.These diaphragms are prone to fail, and could be also blocked by dirt, sand etc. i.e., they could sometimes work as intended, but could fail if the pressure difference of both sides upstream and downstream of the BFP is changed.

And a BFP can also alternate between various jamming status in case of BFP that do not work with a diaphragm, but with a spring loaded solid tiny disk as closing element.