F9 to F0 Low

Glow-worm F9 to F0 Fault Code

Also written as F9TOF0 — same fault.

The Glow-worm F9 to F0 fault code means: your boiler is displaying its recent history of errors to help a technician understand what has gone wrong in the past.. It appears on 1 Glow-worm model 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: Fault history (scrolls through the last 10 faults recorded)

What causes the Glow-worm F9 to F0 fault?

This code is not a specific mechanical failure, but rather a diagnostic mode that displays the boiler's memory of recent issues. It occurs when a technician accesses the internal settings to see a log of the last ten errors the system encountered. By showing these historical codes, the boiler helps the engineer pinpoint recurring patterns or past problems that might be related to the current fault.

DIY fix possible

Press the 'Reset' button to return the boiler to its normal operating modeObserve if a specific fault code reappears after the resetNote down the most recent codes to tell an engineer if the boiler stops working again

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Glow-worm models that show the F9 to F0 fault code

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

Source

Glow-worm F9 to F0 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