Sorry I never finished.
I have rectified the solar water heater problem and am now looking at the heat pump.
I want to control the on period of the pump. In the instructions it is possible to set only one time period and I want two. In the circuit diagram of the controller it shows two connections labelled "Ext", and says this can be connected to an external timer or thermostat. My question is, can I just connect a timer to these terminals? I assume that for the pump to run they must be shorted?