What type of system do you have? I have the same problem and I'm not sure exactly whats causing it yet but imine is a sealed system with a megaflo tank and if I set the slider on the motorised valve to manual the boiler fires up and heats the hot water, I have two motorised valves, one for heating (adjacent to the boiler)and one for hot water (adjacent to the hot water tank)
I'm pretty sure the problem for me anyway is on the electrical side
John, May 2009
