BoilerFaultCodesYour boiler is currently running in a special engineer-only testing mode used to check combustion levels, meaning it is not in its normal operating state.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: CO function active
What causes this fault?
This status is triggered when the selector dial has been turned to the 'CO' position, which is a dedicated mode for engineers to test if the gas is burning safely. It usually occurs because the dial was accidentally left in this position after a service or because the knob has been moved during cleaning. It is not an internal component failure, but rather the boiler obeying a specific manual command.
DIY fix possible
Locate the mode selector switch on the front control panelEnsure the selector is not left in the 'service' or 'test' positionTurn the selector dial to 'OFF' for a few seconds, then back to your desired 'Heating and Hot Water' setting
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