BoilerFaultCodesGlow-worm S.17 Fault Code
Also written as S17 — same fault.
The Glow-worm S.17 fault code means: your boiler is continuing to circulate water after the heating or hot water has been turned off to safely dissipate excess heat.. It appears on 9 Glow-worm models in our database.
Technical description: pump overrun
What causes the Glow-worm S.17 fault?
This occurs when the boiler needs to move residual heat away from the internal heat exchanger after the burner has switched off. It is a standard safety function designed to protect the internal components from overheating and to prevent the water from boiling inside the pipes. If this remains on the screen for an unusually long time, it may indicate that water is not flowing freely through your system bypass.
DIY fix possible
Check that at least one radiator (typically the one in the hallway with no thermostat) is turned fully on.Ensure your magnetic system filter, if fitted, is not blocked.Wait up to 10 minutes to see if the code clears automatically as the system cools down.
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Gas Safe Register →Glow-worm models that show the S.17 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm S.17 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