Done what you said, but had the pump inlet in a bucket of water and the outlet running into the same bucket, all ok, put a tap on the outlet and turned it off and on a couple of times, pump shut off when tap closed. Wound the whole 100m of hose out and plugged the reel inlet back on, switched pump on, it built up pressure then shut off. Turned the water flow on and all ok, shut off flow, and pump shut off as pressure was reached, so hopefully its sorted. Thanks Don