S.13 High

Glow-worm S.13 Fault Code

Also written as S13 — same fault.

The Glow-worm S.13 fault code means: your boiler is struggling to light the gas flame and is currently stuck in the ignition phase.. It appears on 25 Glow-worm 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

What causes the Glow-worm S.13 fault?

This fault occurs when the boiler's internal computer tries to start the combustion process but cannot confirm that a flame has successfully lit. This is usually caused by a buildup of carbon on the ignition probes or a mechanical failure in the gas valve that prevents fuel from reaching the burner. Without a sustained flame being detected, the system stays in this phase to prevent unburnt gas from building up.

Typical repair cost £100-£350 (including labour)

DIY fix possible

Check that your gas prepayment meter has credit (if applicable)Verify that other gas appliances, such as a hob, are working correctlyReset the boiler by pressing the reset button to see if it clears the fault

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Glow-worm models that show the S.13 fault code

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

Source

Glow-worm S.13 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026