I have a pressure pump installed on roof below water tank to boost water head for instant water heaters & showers. It has a 1/2 HP motor & a pressure switch/sensor to operate pump when any tap is opened. However it keeps on starting after every few minutes for half a minute & then stops, even when all taps are closed. Initially I thought of leakages in pipeline but now I shut off the valve on the outlet line of the pump and it still kept on starting and stopping. Can any one advise on the problem please?