Plumbers, I have a peculiar water-hammering issue and I'm wondering where to install arrestors.
It's triggered only at the hot valve in 2nd floor bathroom, when we shut off a whole bunch of different water outlets in the house. It's loud and hard, causes the hot shower valve to get loose, with water running, and the only way to stop it is to turn that particular valve off. The hammering valve is on a tiled wall and breaking open that wall is the least favorite option for me.
It's exactly a single hard "thunk" when we shut a bunch of hot valves, or run machines: the washing machine, hot sides of the two sinks right next to the shower (all these on second floor), kitchen sink hot valve, bathroom sink hot valve, toilet flush and the dishwasher (all these on first floor).
Exactly at the moment of the "thunk" we feel in the valves we shut, or run the machines, the pipe behind the hot shower valve starts hammering, it gets loose, water starts running, and we need to run to that bathroom to turn the loose valve off. Fun fact tho: the toilet right next to the hammering shower valve never triggers the hammering. But the hot valves in the sinks next to the toilet do trigger it.
Edit: Now the "hammering" loud vibration starts randomly without a trigger, at night or day, out of the blue. In this case, I'm not sure it's still "hammering"? And I wonder arrestors will help. I'd really appreciate suggestions, thanks!