BoilerFaultCodesGlow-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 9 Glow-worm models in our database.
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.
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
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →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 27 April 2026