S.30 Low

Glow-worm S.30 Fault Code

Also written as S30 — same fault.

The Glow-worm S.30 fault code means: your boiler is working fine but hasn't started the heating because your external thermostat or timer is currently telling it to stay off.. It appears on 12 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: No Heating demand from external controls 230V

What causes the Glow-worm S.30 fault?

This status code occurs because the boiler's internal computer is waiting for a signal from your wall thermostat or timer before it begins heating your radiators. The most common reason is simply that the room temperature is already higher than the setting on your thermostat, or your heating schedule is currently set to an 'off' period. It can also be caused by flat batteries in a wireless thermostat preventing the 'switch on' signal from reaching the boiler.

This code is frequently seen during the transition into autumn, when homeowners first try to turn their heating on only to find their thermostat batteries have died over the summer.

Typical repair cost £0-120 (including labour)

DIY fix possible

Check that your room thermostat is turned up higher than the current room temperature.Ensure your programmer or central heating timer is set to 'On' or 'Auto'.Replace the batteries in your wireless wall thermostat if the screen is blank or showing a low battery symbol.

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Glow-worm models that show the S.30 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Glow-worm S.30 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