A03 High
Your boiler has likely overheated because the water is not circulating properly or a sensor has detected a temperature that is too high.
Technical description: High limit protection – flow temperature sensor not active, incorrectly located or no system circulation. Check the position of the flow sensor or check pump and radiator valves
Typical repair cost: £120-300 (including labour)
DIY fix possible
Check that your radiator valves are openEnsure there is enough water pressure on the gauge (usually 1.0 to 1.5 bar)Try resetting the boiler using the 'R' button once it has cooled down
Protect yourself from future repair bills
A boiler cover plan would cover faults like A03 — no call-out fees, no surprises.
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Parts commonly replaced
- Circulation Pump
- Limit Thermostat
- Flow Temperature Sensor
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