S.26 Low

Glow-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 25 Glow-worm models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

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.

Typical repair cost £0-120 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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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 7 July 2026