BoilerFaultCodesGlow-worm S.05 Fault Code
Also written as S05 — same fault.
The Glow-worm S.05 fault code means: your boiler is simply cooling itself down after finishing a heating or hot water cycle and will restart normally once it has finished.. It appears on 12 Glow-worm models in our database.
Technical description: pump / fan overrun
What causes the Glow-worm S.05 fault?
This occurs when the boiler has reached its required temperature and needs to shift excess heat away from the internal heat exchanger. The pump and fan continue to run for a short period to prevent the unit from overheating and to protect the internal components. It is a natural part of the boiler's operating cycle and indicates the system is managing its temperature correctly.
DIY fix possible
Wait for the boiler to complete its cooling cycle, which usually takes several minutes.Ensure your internal radiator valves (TRVs) are open to allow water to circulate.Check that the system pressure is between 1.0 and 1.5 bar on the display.
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Gas Safe Register →Glow-worm models that show the S.05 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm S.05 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