Thermostat Fault
Grant
Boiler Thermostat or Control Thermistor Failure
Boiler does not respond to temperature changes, runs too hot or not hot enough, or cycles rapidly.
Advertisements
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Advertisements
Possible Causes
Faulty boiler control thermostat, Stuck relay on PCB, Misreading thermistor, Incorrect wiring to external controls
How to Fix / Troubleshooting
Safety: Isolate power before accessing control wiring or thermostats.
User checks:
- Verify that the room thermostat and any cylinder thermostat are set to appropriate temperatures and calling for heat.
- Ensure the programmer/timer is in an ON or timed period.
Engineer checks:
- Test the boiler control thermostat or thermistor for correct operation using a multimeter and temperature reference.
- Check for stuck relays on the PCB that may be holding the burner on or off.
- Verify correct wiring of external controls to the Grant boiler terminal strip, ensuring no permanent live is bypassing controls.
- Replace any faulty thermostat or thermistor with a Grant-approved component.
Advertisements
Repair Difficulty
Medium
3/5
Required Part
Boiler control thermostat
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements