Limit Thermostat Fault
The safety limit thermostat has activated or has a fault. This can indicate the boiler is overheating or the thermostat itself has failed.
Step-by-Step Fix Guide
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Step 1
Turn off the boiler and allow to cool for 30 minutes
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Step 2
Check system pressure and bleed radiators
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Step 3
Reset once
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Step 4 Engineer only
If A02 returns, call a Gas Safe engineer to test the limit thermostat and check circulation
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.