Red LED illuminated (Lockout) Emergency

Potterton Red LED illuminated (Lockout) Fault Code

Also written as REDLEDILLUMINATEDLOCKOUT — same fault.

The Potterton Red LED illuminated (Lockout) fault code means: your boiler has shut down because a safety sensor has detected that dangerous exhaust fumes are not escaping through the chimney correctly.. It appears on 2 Potterton models in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: The Products Discharge Safety Device (TTB) has operated in the case of flue blockage and the boiler has gone to lockout.

What causes the Potterton Red LED illuminated (Lockout) fault?

This fault occurs when a safety sensor detects that combustion gases are blowing back into the room instead of escaping through the chimney. The most common reasons are a blockage in the chimney, such as a bird's nest or debris, or severe atmospheric conditions preventing the natural flow of exhaust. The boiler shuts down immediately to prevent harmful carbon monoxide from entering your home.

This fault is more frequent during periods of high winds or extreme cold, which can create pressure imbalances or 'downdraughts' in the chimney flue.

Typical repair cost £100-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Potterton models that show the Red LED illuminated (Lockout) fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Potterton Red LED illuminated (Lockout) 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