suddenly our system misbehaving. When the hot water is active then the cental heating pipes warm up too and the thermostat wont swith the boilder off though it still clicks. Even if we have hot water on only the cental heating radiators still heat up. I presume there is a thermostat problem...or is it worse...its a potterton gas fired fanned balanced flue gas fired
what thermostat wont switch the boiler off, the room thermostat or the boiler stat ? if radiators are heating up when only the hot water is selected, its a problem with the actuator, or 3 port valve. Remove the actuator and select water only, then heating only, make sure the valve turns, also check spindle on three port valve is free to move.