Thanks for the reply, the ball valve is not running all the time, and the water level is higher in the radiator top up tank. The water in the cylinder only gets slightly warm, whereas the water coming from the boiler up through the top up tank is boiling. I would have thought the boiler stat...
My boiler does not cut out, appears to be overheating and hot water is filling up radiator top up tank and causing overflow. I have changed boiler thermostat, anybody have any suggestions.