0A3 High
Your boiler has switched itself off because it has reached an unsafe temperature to prevent damage to the internal components.
Technical description: Overheat thermostat lock-out
Typical repair cost: £120-350 (including labour)
DIY fix possible
Check that all radiator valves are fully open to allow water to circulate.Ensure there is enough water pressure in the system (typically 1.0 to 1.5 bar).Press and hold the reset button for 2-5 seconds to see if the system restarts.
Protect yourself from future repair bills
A boiler cover plan would cover faults like 0A3 — no call-out fees, no surprises.
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Parts commonly replaced
- Circulation Pump
- Overheat Thermostat
- Main Heat Exchanger cleaning/flush
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