BoilerFaultCodesVokera A20 Fault Code
The Vokera A20 fault code means: your boiler is detecting a flame remaining inside the unit for a few seconds after it should have been shut off.. It appears on 4 Vokera models in our database.
Technical description: The flame is extinguished too late after the gas valve closes
What causes the Vokera A20 fault?
This fault occurs when the boiler's sensors detect a flame for several seconds after the heating cycle has finished and the gas should have stopped flowing. The most common reason is a gas valve that is physically sticking open or an electrical fault in the control board that fails to cut power to the valve. In some cases, a carbon-coated sensing electrode may also be providing a false signal back to the boiler.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vokera models that show the A20 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera A20 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