A CO Low

Vokera A CO Fault Code

Also written as ACO — same fault.

The Vokera A CO fault code means: your boiler has been accidentally switched into a specific testing mode used by engineers to check exhaust fumes, and it is not currently operating in normal heating mode.. It appears on 1 Vokera model in our database.

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 test
Typical repair cost £80-120 (including labour)

DIY fix possible

Locate the chimney sweep or manual test button on the control panelPress or toggle this button to exit the combustion analysis modeTurn the boiler off at the mains for 60 seconds and then switch it back on to reset the system

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Vokera models that show the A CO fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vokera A CO fault code information on this page is sourced and cross-checked against the official Vokera service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026