BoilerFaultCodesPotterton LOCKOUT: c Fault Code
Also written as LOCKOUTC — same fault.
The Potterton LOCKOUT: c fault code means: your heater has shut down because it cannot pull in enough fresh air to operate safely, which increases the risk of dangerous carbon monoxide buildup.. It appears on 2 Potterton models in our database.
Technical description: INADEQUATE ROOM VENTILATION
What causes the Potterton LOCKOUT: c fault?
This fault occurs when the appliance detects that there isn't enough fresh air entering the room to support safe combustion. The most common reasons are air vents being accidentally blocked by furniture, a buildup of dust and lint in the grilles, or even new home improvements like weather-stripping or double glazing that have made the room too airtight.
This fault is more common in winter when homeowners may inadvertently block air vents to stop cold draughts or keep windows tightly shut for long periods.
DIY fix possible
Check all external air vents or bricks for obstructions like leaves, debris, or bird nestsEnsure vents are not covered by furniture, curtains, or new building workClean the external air grille to remove dust or lint buildupPerform a reset as per manufacturer instructions once ventilation is verified as clear
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Gas Safe Register →Potterton models that show the LOCKOUT: c fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton LOCKOUT: c 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