E23
Keston
Manual Reset Overheat Thermostat Trip
Boiler shows E23, safety thermostat has tripped and must be manually reset
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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.
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Possible Causes
Severe overheating due to pump failure, Blocked heat exchanger, Airlock, Faulty thermostat
How to Fix / Troubleshooting
Safety: Do not repeatedly reset an overheat thermostat without finding the cause. Risk of serious damage or scalding.
User checks:
- Allow the boiler to cool completely. Do not attempt to remove the case yourself unless permitted in the user manual.
- Contact a Gas Safe engineer to investigate the cause of overheating.
Engineer checks:
- Identify and press the manual reset button on the Keston overheat thermostat if accessible, after confirming the system has cooled.
- Check pump operation, system pressure, and for blockages or closed valves.
- Inspect the primary heat exchanger for scale or sludge and clean/replace as needed.
- Test the overheat thermostat for correct operation and replace if nuisance tripping without cause.
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Repair Difficulty
Hard
4/5
Required Part
Overheat Thermostat
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