A03 High
Your boiler has likely overheated because the water isn't moving through the system properly or a safety sensor has detected a temperature that is too high.
Technical description: High limit protection – possible flow temperature sensor not active or incorrectly located, no system circulation
Typical repair cost: £120-300 (including labour)
DIY fix possible
Check that your radiator valves and isolation valves are fully openEnsure your system pressure is topped up to between 1 and 1.5 barPress the Reset button on the control panel to see if the fault clears
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
- Overheat thermostat
- Flow temperature sensor (NTC)
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