My central heating is controlled by a wireless room thermostat (Honeywell HCW80) and the receiver/relay unit (HC60NG) which triggers the zone valve actuator. The system has worked perfectly for years but now has a problem. When the thermostat calls for heat the relay receives the signal (green light on) and initially triggers the actuator but within a second or so then cuts the power and the actuator returns to the closed position. I can hear the relay click 'on' then almost immediately click 'off' again. I've tested the power supply to the actuator with a meter and sure enough power comes on briefly then goes off. Checked the actuator and zone valve and both appear to work perfectly. Presumably the relay is faulty and needs to be replaced but wanted to be sure there could be no other reason for this behaviour before spending £90+ on a replacement.
Any advice would be much appreciated.
Any advice would be much appreciated.