Medium Lockout
Preheat control neon flashing on Potterton Performa 24

Your boiler has detected an internal communication error or a disconnected jumper wire, which usually prevents the preheat function or the boiler from operating correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Go to section ‘L’: Check continuity of loop on A10 connector.

What causes this fault?

This fault occurs when the boiler's main control board loses its connection to a specific internal bypass wire that tells it how to manage the preheat function. It is usually caused by a loose connection at the 'A10' plug or a physical break in the wiring harness, which prevents the boiler from completing its safety checks. In some cases, the internal electronics on the printed circuit board may have failed, meaning it can no longer 'see' the loop even if the wire is intact.

Engineer required

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

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