neon '12' illuminated High

Ideal neon '12' illuminated Fault Code

Also written as NEON12ILLUMINATED — same fault.

The Ideal neon '12' illuminated fault code means: your boiler has detected that a vital internal temperature sensor is disconnected or has failed, preventing it from heating your home safely.. It appears on 1 Ideal model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Sensor (NTC) removed from P.C.B. and thermostat neon '12' is illuminated.
Typical repair cost £90-180 (including labour)

Engineer required

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

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Ideal models that show the neon '12' illuminated fault code

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

Source

Ideal neon '12' illuminated fault code information on this page is sourced and cross-checked against the official Ideal service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026