BoilerFaultCodesGlow-worm S.26 Fault Code
Also written as S26 — same fault.
The Glow-worm S.26 fault code means: your boiler's internal cooling fan is staying on longer than expected after the heating has switched off.. It appears on 9 Glow-worm models in our database.
Technical description: fan overrun
What causes the Glow-worm S.26 fault?
This status occurs when the internal fan continues to run for an extended period after the boiler has stopped firing to dissipate excess heat from the heat exchanger. It is often caused by heat lingering in the system due to poor water circulation or a pump that isn't moving hot water away fast enough. In some cases, it can also be a sign that the main control board is misreading the temperature sensors.
This is more common during winter months when the boiler is running at higher temperatures for longer periods, leading to more residual heat that needs to be cleared.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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.26 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm S.26 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