After 2 hours, I still had water trickling from the pipe ( about 1-2 GPH) , so I opted for SharkBite valves just to get the job done. In thinking about this, I believe I have some crossflow happening, and would like some help in a method for tracking this down.

The house is 4150 sq ft single level, with copper pipes buried in the slab. 5 bathroom showers, all with Moen single handle valves. Two of them are the Moentrol valves with balancing spools. The other three appear to be the more basic valve. I also have 4 sinks with single handle faucets ( two are Moen, One Price-Phister, the other unknown( installed behind the mirror of the bathroom sink!) . I’m focusing on the single handle installs, think this is the most likely place for crossflow to happen. There is no “Y” connector on the washing machine.

I’m thinking that I will remove the pump again ( easier now!) and after allowing the pipes to drain, begin shutting off the cold water supply at each of the single handle installations to see if the flow decreases/stops. Assume that any change means crossflow in that fixture, and a cartridge replacement might be the fix.

Anybody have other ideas? Would a sticking Moentrol Balancing Valve cause this issue?