I have a Worcester Bosch Highflow 400. The pump seems to be working ok. I removed the head and the impellor is still attached and spinning freely. Both the inlet and the outlet from the pump heat up. I removed the diverter valve and part stripped it. There was a few bits of dirt in it but not much. The diaphragm at the back seems ok. I'm at a loss as to the reason so any help would be most appreciated.. Thanks.