My neighbour has a Potterton Prima F boiler (not combi) the problem is that they can only get the central heating on when the water in the cylinder requires heating. If you run hot water off or turn the thermostat up then the pump and boiler will kick in and all is well. But as soon as the demand for hot water is satisfied then the pump and boiler shuts down and no central heating even though the required room temp has not been reached.
Could it be that the three port valve is faulty or could it be the PCB in the boiler?
Could it be that the three port valve is faulty or could it be the PCB in the boiler?