BoilerFaultCodesWhat the manual says
Manufacturer manualThe boiler will now enter the combustion analysis mode (CO mode) for a period of 15 minutes. During this time it will remain on full gas and “CO” will be displayed on the LED display.
What causes this fault?
This code appears when the boiler has been manually put into a specific testing state by an engineer, often during an annual service. It is physically triggered by turning a dial or sequence on the control panel to allow the gas levels to be measured accurately. It is not a breakdown, but rather a temporary override of the boiler's normal temperature controls.
DIY fix possible
Wait 15 minutes for the test mode to time out automaticallyTurn the mode selector dial to 'OFF' for a few seconds and then back to 'ON'Check if the selector dial was accidentally left in the 'Service' or 'CO' 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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