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Message: <blockquote data-quote="user 29611" data-source="post: 453809" data-attributes="member: 29611">This alone would make the difference when the heating has been on. Once the valve is open the micro switch in the valve is closed. Whilst the hot water is on and calling the boiler for heat you will get a back feed from the boiler down the orange to the heating valve, through the micro switch and to the grey which is in the same terminal as the brown, therefore giving the valve motor power to remain open, even though the heating timer and thermostat is off. This would then revert back to normal operation once there was no demand for the boiler from the hot water.If the radiators became hot when the hot water was on, without the heating thermostat being on then yes there would most likely be something else causing this. But either way the grey wires should always be permanent live and be separated from the brown's by a time or thermostat switch somewhere.</blockquote>