Many thanks. I think there must be a bug within the Vaillant system that causes the wireless system to not only disconnect but then not reconnect. In my case it occurs about twice, maybe three times a year, at which point the house can reach 30 degrees mid winter (the manual instructs that the boiler temperature control be set to max). Vaillant suggest moving the wireless receiver away from the boiler which indicates that the signal is weak or else there is interference from the boiler. Is there any specific information about how or why such an rare, intermittent fault is happening. If the signal is weak or there is interference from the boiler I would expect more regular failures. By the way the boiler is in a cupboard with a painted MFD door. I have had the metal cover removed from the bottom of the boiler. The thermostat is next to the door in the front room, downstairs and the boiler is in the backroom, downstairs. Just two doors including the cupboard between them and total distance is about 5 metres. Right now everything is working fine. When the fault occurs, I turn off the boiler, turn it back on, press the button on the receiver and eventually it starts working as normal