BoilerFaultCodesGlow-worm S.34 Fault Code
Also written as S34 — same fault.
The Glow-worm S.34 fault code means: your boiler is not broken; it has simply noticed the temperature is very low and is running briefly to prevent the internal pipes from freezing.. It appears on 12 Glow-worm models in our database.
Technical description: frost protection active (Priority 4)
What causes the Glow-worm S.34 fault?
This status occurs when the temperature sensor inside the boiler detects that the water has dropped below a certain threshold, typically around 5°C. To prevent the heat exchanger from cracking due to ice, the boiler automatically fires the burner to gently warm the internal components. It is a safety feature designed to protect your heating system during periods of extreme cold.
This code will almost exclusively appear during the winter months when outdoor temperatures drop near or below freezing.
DIY fix possible
No action is required as this is a normal safety function.Ensure your thermostat is turned up if you want the heating to stay on.Check that any visible external pipes are properly insulated to prevent freezing.
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Gas Safe Register →Glow-worm models that show the S.34 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm S.34 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