I've moved into a house with a potterton suprima 40 boiler and an unvented hot water system. After a few nights I noticed that the pump runs all the time even when there are no demands for CH or HW. All the wiring seems to be going to all the right places and there are two, 2 way valves in the system (one each for CH & HW). I've changed the PCB and it's still happening. Any ideas?