I've got ideas about what is causing the problem but never seen it before. Standard single lever Delta shower valve with the plastic cartridge inside. I've removed the bonnet and replaced the springs and rubber thingys. That worked for a while. At first it happened when the toilet was flushed then the water in the shower came on and stayed on...then a month after the fix the washing machine was turned on and the same thing, water comes on in the shower again and doesn't go off. I thought maybe it was something to do with water pressure but it's 75 psi. To me this might be some kind of problem where a venturi effect is created but I don't have a clue how to fix it and KNOW that the fix will work. I'm thinking that either installing a new cartridge will do it...but that is only a guess...but something needs to be installed in a line somewhere to prevent the water's action on the valve. Maybe an expansion tank or water hammer preventer is needed... any ideas guys & gals?
