BoilerFaultCodesWhat the manual says
Manufacturer manualConfirms the appliance is in combustion test mode
What causes this fault?
This code appears when the boiler is placed into a specific 'test mode' used for measuring gas emissions and performance. It is physically triggered when the selector dial is moved to the 'CO' position or during the initial startup sequence. It does not indicate a mechanical failure, but rather that the boiler is temporarily overriding its normal sensors to run at a consistent output.
This code is most frequently seen during Autumn or Spring when boilers are more likely to undergo their annual safety inspections and servicing.
DIY fix possible
Wait for the engineer to finish the service modeTurn the mode selector dial away from the 'test' or 'CO' position to the hot water or heating settingIf the code persists, try resetting the boiler by turning the dial to off/reset and back to the on position
Avoid the next call-out bill
A cover plan would handle faults like CO: no call-out fees, no surprise bills.
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