How to check heat pump / controller

Hi. I have a NEFF S51E50X1GB. It has stopped heating - though the washing cycle completes. I have taken out the PCB - and can’t see any damage. I put the controller back in - and it heated for one wash - now it doesn’t again. I guess therefore it is not the heat pump - but how do I check this? ….. Can I check voltages to the pump? If so - which wires (I am guessing the bigger red/black? Any suggestions? (Happy to buy a new controller - but it is expensive if it is not the cause)