BoilerFaultCodesPotterton A20 Fault Code
The Potterton A20 fault code means: your boiler is detecting a flame at the wrong time, suggesting that gas might be leaking into the burner when it should be shut off.. It appears on 2 Potterton models in our database.
Technical description: Flame detected during ignition cycle. Check gas valve closes fully. Replace. Check ionisation probe & condensate outlet
What causes the Potterton A20 fault?
This fault occurs when the boiler's sensors detect a flame while the gas valve should be closed, or it senses a 'ghost flame' due to an electrical error. The most common reason is a faulty gas valve that is failing to shut off properly, causing gas to linger in the burner. It can also be triggered by a contaminated sensor probe that is sending an incorrect electrical signal to the main control board.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Potterton models that show the A20 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton A20 fault code information on this page is sourced and cross-checked against the official Potterton service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026