S.23 High

Heatline S.23 Fault Code

Also written as S23 — same fault.

The Heatline S.23 fault code means: your boiler is struggling to start the burner to heat your water or radiators because it has detected a problem with the ignition process.. It appears on 8 Heatline models 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: Ignition
Typical repair cost £90-250 (including labour)

Engineer required

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

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Heatline models that show the S.23 fault code

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

Source

Heatline S.23 fault code information on this page is sourced and cross-checked against the official Heatline service / installation manuals for each affected model.

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