BoilerFaultCodesPotterton C.(5) Fault Code
Also written as C5 — same fault.
The Potterton C.(5) fault code means: your boiler's small pilot light is on, but the main burner cannot engage to actually heat your home because the fuel path is obstructed.. It appears on 3 Potterton models in our database.
Technical description: Main burner fails to light, pilot burning - Blocked main burner injector.
What causes the Potterton C.(5) fault?
This fault occurs when debris or soot builds up inside the tiny hole of the main burner injector, physically blocking the gas from reaching the burner. While the pilot light stays lit to prove there is a flame, the blockage prevents the main fire from starting, meaning the boiler cannot produce heat for your radiators or water. The most common reason is a buildup of carbon or microscopic dust particles over several years of operation.
This issue often comes to light during the first cold spell of autumn, as the burner is required to run for longer periods and at higher capacities after being mostly dormant over the summer.
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 C.(5) fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton C.(5) 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