Phase reversed neon (behind the knob) lighting High

Malvern Phase reversed neon (behind the knob) lighting Fault Code

Also written as PHASEREVERSEDNEONBEHINDTHEKNOBLIGHTING — same fault.

The Malvern Phase reversed neon (behind the knob) lighting fault code means: your boiler has detected that the incoming electrical wires are connected the wrong way around, preventing it from safely starting the main burner.. It appears on 1 Malvern 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: L and N supply are reversed; the boiler will not progress beyond pilot ignition.
Typical repair cost £80-140 (including labour)

Engineer required

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

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Malvern models that show the Phase reversed neon (behind the knob) lighting fault code

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

Source

Malvern Phase reversed neon (behind the knob) lighting fault code information on this page is sourced and cross-checked against the official Malvern service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026