BoilerFaultCodesPotterton A(4) Fault Code
Also written as A4 — same fault.
The Potterton A(4) fault code means: your boiler is struggling to stay lit because the small starter flame is being blocked by a buildup of soot or debris.. It appears on 3 Potterton models in our database.
Technical description: Blocked pilot injector.
What causes the Potterton A(4) fault?
This fault occurs when the small tube that delivers gas to the starter flame becomes restricted by tiny particles of soot or dust. Without a strong enough pilot flame to heat the safety sensor, the boiler will automatically shut down to prevent gas from leaking into the room. The most common reason is simply a buildup of debris over many years of operation which eventually chokes the gas supply to the burner.
This issue often comes to light in autumn when the boiler is switched back on after being idle during the summer, allowing dust to settle and harden in the injector.
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(4) fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton A(4) 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