Flashing red A or B High
Your boiler has switched itself off because it has detected that it is getting too hot or a temperature sensor has failed.
Technical description: Overheat thermostat has operated / Temperature sensor fault
Typical repair cost: £100-220 (including labour)
DIY fix possible
Check that your radiator valves are open to allow water to flowCheck that your system pressure is between 1 and 1.5 bar on the gaugeTurn the selector switch to the 'Reset' position for a few seconds and then back to 'On'
Protect yourself from future repair bills
A boiler cover plan would cover faults like Flashing red A or B — no call-out fees, no surprises.
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Parts commonly replaced
- Overheat Thermostat
- NTC Temperature Sensor
- Circulation Pump
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