Worcester 240. Flood Damage, Sequence of operation?

I am trying to fix my daughters Boiler. There was a flood and the boiler stopped working. I have dried out the Boiler and now it doesn't trip the mains all the time.
I have replaced the main PCB and the micro switch loom. I know the pump and the fan are working ok, but the Boiler still trips the mains when the hot water is turned on. It feels I have missed somthing basic I think I have traced it to the flow switch cct but I need to know the sequence of operations to get further.