BoilerFaultCodesGlow-worm S.16 Fault Code
Also written as S16 — same fault.
The Glow-worm S.16 fault code means: your boiler is performing a routine cooling cycle to clear internal gases after a burst of activity and is not currently in a fault state.. It appears on 9 Glow-worm models in our database.
Technical description: fan overrun
What causes the Glow-worm S.16 fault?
This occurs when the boiler’s fan continues to run after the burner has switched off to safely purge remaining heat and combustion gases from the unit. It is a normal safety process that typically happens after a period of intense heating or hot water demand to ensure the internal components cool down correctly. Your boiler hasn't broken down; it is simply finishing its work cycle before it can start again.
DIY fix possible
Wait for 5-10 minutes to allow the cooling cycle to completeEnsure your thermostat is not calling for heat if you want the fan to stop soonerCheck that the boiler display changes to a different code after the cooling period
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Gas Safe Register →Glow-worm models that show the S.16 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm S.16 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