Low Information
CO on Vokera Syntesi 25

Your boiler is currently running in a special engineer-only testing mode for checking gas emissions and is not experiencing a mechanical fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

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

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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