BoilerFaultCodesTechnical description
combustion analysis mode (CO mode)
What causes this fault?
This code appears when the boiler has been manually put into a dedicated testing mode, typically by an engineer turning a selector switch or pressing a specific button sequence. It is designed to override normal thermostat controls so the boiler runs at a fixed rate, allowing for accurate measurement of gas combustion levels. It is not triggered by a component failure, but rather by the system being told to perform a functional test.
DIY fix possible
Turn the selector dial to the 'OFF/RESET' position.Wait approximately 10 seconds.Turn the selector dial back to your desired setting (Heating/Hot Water).
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