What is this?
When your smart thermostat shows it is calling for heat but the heating does not come on (or vice versa), the thermostat is not properly controlling the heating system. The thermostat display may look normal, the app may work, but the actual heating does not follow the commands.
Common causes
- Receiver relay has failed — thermostat sends signal but relay does not switch
- Wireless signal not reaching the receiver from the thermostat
- Incorrect wiring during installation
- Motorised valve stuck or failed (not opening when called)
- Boiler not responding to the call for heat
- Thermostat paired to the wrong receiver or zone
Is it dangerous?
Not dangerous, but leaving heating uncontrolled can waste significant energy if the heating runs constantly, or cause comfort issues if it does not come on when needed. In very cold weather, lack of heating could lead to frozen pipes.
Can I fix it myself?
Check the receiver unit near the boiler — when the thermostat calls for heat, the receiver should click and a light should come on. If the receiver does not respond, try re-pairing the thermostat and receiver following the manufacturer's instructions. Check that the boiler is set to accept thermostat control rather than continuous operation.
When to call an electrician
Call an electrician if re-pairing does not fix the issue, if the receiver clicks but the heating does not start, if the system worked before and has stopped without any changes, or if the thermostat was recently installed.
What will an electrician do?
Test the wireless signal between thermostat and receiver
Check the receiver relay output with a multimeter
Verify the wiring between receiver, boiler, and any motorised valves
Test motorised valves for correct operation
Replace the receiver unit or re-wire as needed
Typical cost
£80 – £250
Receiver replacement is the most common fix. If motorised valves also need attention, costs will be higher. Wiring corrections after a poor installation may take additional time.
