Glow-worm · Energy
F.23 boiler fault code
Energy
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What F.23 means
Safety switch-off: the temperature difference between sensors NTC1 and NTC2 is too great.
Safe check
Record the exact display and model from the outside label or manual. Do not open the boiler or attempt an internal sensor or pump check.
When to contact an engineer
The temperature-sensor or circulation diagnosis requires a Gas Safe registered engineer; contact one if this code appears or returns.
Safety notice
A boiler fault code alone is not a gas or carbon-monoxide emergency. If you smell gas, a CO alarm sounds, anyone feels unwell, or there is an unsafe flame, leave and call 0800 111 999 from outside.
Source and provenance
- Energy range fault codes
manufacturer trade support table
Checked 27 September 2026; the online page publishes no revision