How much does it cost to fix Baxi error code FLASH OFF ON?

Typical repair cost for the Baxi FLASH OFF ON fault is £100-280 including labour.

FLASH OFF ON High

Baxi FLASH OFF ON Fault Code

Q: What does the Baxi FLASH OFF ON fault code mean?

Your boiler has shut down because it has become too hot and needs to be safely reset after cooling down.

Also written as FLASHOFFON — same fault.

The Baxi FLASH OFF ON fault code means: your boiler has shut down because it has become too hot and needs to be safely reset after cooling down.. It appears on 24 Baxi models in our database.

Technical description: Overheat lockout

What causes the Baxi FLASH OFF ON fault?

This fault occurs when the water inside the heat exchanger exceeds a safe temperature limit, triggering a safety cutout to prevent damage. The most common reasons include a failing circulation pump that isn't moving heat away quickly enough or a blockage in the system pipework. It can also be caused by a faulty internal sensor incorrectly reading the temperature.

This issue often surfaces during the first cold spell of autumn when the heating is turned on after being dormant all summer, which can cause internal pump components to seize.

Typical repair cost £100-280 (including labour)

DIY fix possible

Turn the boiler thermostat knob to the 'OFF' position.Wait at least 10 seconds for the system to acknowledge the reset.Turn the thermostat knob back to your desired temperature setting.

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Baxi models that show the FLASH OFF ON fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Baxi FLASH OFF ON fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026