BoilerFaultCodesPotterton LOCKOUT: a Fault Code
Also written as LOCKOUTA — same fault.
The Potterton LOCKOUT: a fault code means: your boiler's small starter flame has become blocked by dust or debris, preventing the main heating system from firing up.. It appears on 2 Potterton models in our database.
Technical description: BLOCKED PILOT
What causes the Potterton LOCKOUT: a fault?
This fault occurs when the tiny opening that fuels the starter flame becomes clogged with household dust, lint, or carbon build-up. Without a steady pilot flame to heat the internal safety sensor, the boiler will refuse to light the main burner as a security precaution. The most common reason is simply a lack of regular servicing, allowing debris to accumulate over time until the gas flow is restricted.
This issue often surfaces in autumn when the boiler is switched back on after being idle during the summer months, allowing dust to settle and harden in the pilot assembly.
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 LOCKOUT: a fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton LOCKOUT: a 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