Being as everybody seems to be talking everything but footy..... My central heating timer goes completely bonkers if I try to run both the heating and hot water. Works fine if I only run one or the other. I replaced the original timer (because the sliding controls were buggered) with a digital version having carefully photographed the wiring first. Any ideas would be most welcome.
Is there a motorised control valve directing the boiler output water to either the hot water cylinder or the central heating? If there is it sounds like it's stuck in the middle.