BoilerFaultCodesPotterton Lockout (Red) flashing Fault Code
Also written as LOCKOUTREDFLASHING — same fault.
The Potterton Lockout (Red) flashing fault code means: your boiler has sensed it is getting too hot and has shut itself down as a safety precaution.. It appears on 1 Potterton model in our database.
Technical description: Overheat condition occurs
What causes the Potterton Lockout (Red) flashing fault?
This fault happens when water inside the boiler reaches a temperature that is no longer safe, triggering an automatic shutdown to prevent damage. It is usually caused by a pump failure preventing water from moving away from the heat exchanger, or a build-up of sludge and debris that blocks the flow. In some cases, a faulty sensor might also incorrectly signal that the system is overheating.
This issue often surfaces in autumn when the heating is turned on for the first time after summer, as internal pump parts can seize during long periods of inactivity.
DIY fix possible
Check that all radiator valves are fully open to allow water to flow.Ensure the system pressure is between 1 and 1.5 bar on the pressure gauge.Turn the control knob to the 'Reset' position for five seconds and then back to 'On'.
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Gas Safe Register →Potterton models that show the Lockout (Red) flashing fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Potterton Lockout (Red) flashing 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