posted this 22 December 2017
Next time the pump carries on running when the shower is turned off you need to close the isolation valves on the pump. Either inlets or outlets, it doesn't matter on a positive pump. If the pump stops when you close the valves then the pump is ok and you
have water going somewhere which would probably be one of the shower non return valves sticking. If one of the shower valves is faulty the pump will run on when either shower is used, not just the faulty one.
If the pump still runs with the isolation valves closed then the pump is faulty and the most likely thing will be one of the floats sticking in the pump, most likely the hot side. Check the hot water temperature isn't excessive as that can cause that.