Pool heat pump not coming on.

[jamesBen80]

I've just picked up a 2nd hand pool heat pump, its a bit tatty but I was told it just had a faulty water flow switch. I have removed the water flow switch and tested it and it appears to be operating as if I move the paddle in the direction of the water flow it's resistance changes and it closes. However if I hold the flow switch closed simulating a water flow through the heat exchanger and try to turn the heat pump on I still only get a click from a switch on the refrigerant circuit, the fan doesn't even come on? The controller is the usual helpful Chinese affair with no logical menu system and I can't seem to find an online manual that shows my controller. I'm trying to follow the refrigerant pipework to trace which switch is clicking when I power on. Can anyone offer and incite into these things. I don't want to chuck it away if its just a faulty sensor or switch, but I can't see the sense in spending £100's on engineer callouts, when I could put that money towards a new one! looking for refrigerant engineers or AC guys that can point me in the right direction. Thanks