I have recently bought a house with underfloor heating driven by a geothermal heat exchanger, divided into 2 zones - living area and bedroom area. The living area is controlled by a simple Honeywell thermostat fixed to an outside wall. We keep the system running all the time, controlled purely by this thermostat, set to 22C. Unfortunately, in cold weather the thermostat struggles to reach this temperature, probably because of poor insulation in the wall, so the room temperature often climbs to 24C or higher before the thermostat shuts off the system. So I want to fit a wireless thermostat. However, the current Honeywell is battery driven, and only has wiring to turn the heat exchanger on and off, and there is no mains power nearby. So far, all the wireless thermostat I have looked at have receivers that need mains power, which would involve channelling the wall. Any suggestions of makes that have battery driven receivers??