BoilerFaultCodesPotterton A.(3) Fault Code
Also written as A3 — same fault.
The Potterton A.(3) fault code means: your boiler is unable to start because the small starter flame is not lighting, likely due to a tiny blockage in the gas supply line.. It appears on 3 Potterton models in our database.
Technical description: Pilot fails to light - Blocked Pilot Injector.
What causes the Potterton A.(3) fault?
This fault occurs when the tiny orifice in the pilot injector becomes restricted by microscopic debris or carbon buildup, preventing the starter flame from reaching the sensor. Without this stable pilot flame, the boiler’s safety system refuses to open the main gas valve to prevent unburned gas from escaping. The most common reason is simply age-related wear or dust being drawn into the pilot assembly over time.
This issue often surfaces after the summer months when the boiler has been switched off for long periods, allowing dust to settle and solidify within the small pilot pipe.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Potterton models that show the A.(3) fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton A.(3) 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 27 April 2026