F23 High

Heatline F23 Fault Code

The Heatline F23 fault code means: your boiler has detected that the water is not circulating properly, meaning it is getting hot in one area but not moving to the rest of your system fast enough.. It appears on 8 Heatline models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Maximum temperature difference reached between return and fl ow heating
Typical repair cost £150-300 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Heatline models that show the F23 fault code

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

Source

Heatline F23 fault code information on this page is sourced and cross-checked against the official Heatline service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026