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Underfloor Heating Thermostat Not Working
Your underfloor heating thermostat has a blank screen, shows errors, or is not controlling the heating.
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What's happening?
The thermostat is the control centre for your electric underfloor heating. It reads the floor temperature sensor and switches the heating on and off to maintain the set temperature. When the thermostat fails, the heating may not turn on at all, may run continuously, or may display error codes.
What usually causes it?
- Failed floor temperature sensor (most common thermostat-related fault)
- Blown fuse in the spur supplying the thermostat
- Thermostat internal electronics failure
- Loose wiring connections behind the thermostat
- Incorrect thermostat settings or programming
- Incompatible replacement thermostat
Is it dangerous?
A faulty thermostat is not dangerous in itself. However, if the thermostat fails in a way that the heating stays on constantly, the floor could overheat. If the floor feels unusually hot, switch the heating off at the isolator and call an electrician.
Can I fix it myself?
Check the fuse in the spur feeding the thermostat. Try resetting the thermostat to factory settings using the manual. Check the programming and mode settings — many thermostats have holiday or frost-only modes that prevent normal operation. Replace the batteries if it is a wireless thermostat.
When should you call an electrician?
Call an electrician if the thermostat display is blank despite having power, if it shows a sensor error, if the heating runs constantly and will not turn off, or if you need a replacement thermostat installed.
What will the electrician actually do?
- Test the supply to the thermostat
- Measure the floor sensor resistance and compare to the manufacturer's specification
- Check thermostat output to confirm it is switching the heating
- Replace the floor sensor or thermostat as needed
- Program and commission the new thermostat
What will it cost to fix?
£80–£220
Thermostat replacement including a new unit typically costs £120-£200. Floor sensor replacement is cheaper if the sensor cable is accessible.
Find an electricianFrequently asked questions
We’re happy to answer all your questions.
Why does my thermostat show a sensor error?
The floor temperature sensor has either failed or become disconnected. This sensor is a small probe embedded in the floor with a cable running back to the thermostat. An electrician can test it and replace it if needed.
Can I replace the thermostat myself?
Replacing an underfloor heating thermostat involves working on fixed wiring, which should be done by a qualified electrician. Getting it wrong could damage the heating system or create a safety risk.
Will any thermostat work with my underfloor heating?
The replacement thermostat must be compatible with your system's wattage and the type of floor sensor used. An electrician can advise on the right replacement.
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