BoilerFaultCodesGlow-worm 26 Fault Code
The Glow-worm 26 fault code means: your boiler's electronic brain has developed a software or hardware error and can no longer control the heating and hot water safely.. It appears on 1 Glow-worm model in our database.
Technical description: There is an internal fault in the Automatic Control Module.
What causes the Glow-worm 26 fault?
This fault occurs when the boiler's main control board suffers an internal hardware failure or a memory error in its programming. It most commonly happens due to electrical wear over time, but can also be triggered by a sudden power surge or dampness affecting the circuitry.
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 26 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Glow-worm 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