Booster pump/sealed water system issue

[Brend65]

I have a Grundfos MQ3-45 pump fitted on my sealed domestic water system (pump runs when tap, toilet etc is used). The hot water cylinder is located on the middle floor, there is a shower, sink etc on the floor above it. Recently the pump has started to run on its own for 10secs at different times of the day/night. This suggested to me there was either a leak in the pipework/fittings in the house or the pump was faulty. I fitted a gate valve to the outgoing side of the pump. This would isolate the water supply to the house when closed. I verified this valve worked correctly before integrating into the system. With valve closed I could hear the pump run during the night. I fitted new MQ pump but this has not solved the issue! I have checked toilets, taps, showers and all are dry. Any ideas?

 

[Madrab]

it must be that the pump is detecting water movement and the internal switch is activating the pump. It could be on the oncoming mains too, if there is a drop in mains pressure that's creating the movement. Only way to test that would be to have a valve either side and see if it then stops.

 

[Brend65]

Thanks very much for the reply Madrab. Apologies but my knowledge is limited. The pump is fed from overhead tank in attic (gravity??) using 1"copper pipe. There is a gate valve fitted on that pipe just before the pump. Are you saying I should try closing that valve also to test? Do I close both valves together either side?
There is also a non return valve fitted to the copper pipe on the incoming side (feed) of the pump. I replaced that also with a new one as the internals were worn. I also understand that there is a built in non return valve in the pump.