FSK1 Low

Warmflow FSK1 Fault Code

The Warmflow FSK1 fault code means: your boiler has detected that the external frost protection kit has been triggered, which means the system is attempting to protect itself from freezing temperatures.. It appears on 1 Warmflow 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: Frost Thermostat Kit
Typical repair cost £80-150 (including labour)

Engineer required

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

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Warmflow models that show the FSK1 fault code

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

Source

Warmflow FSK1 fault code information on this page is sourced and cross-checked against the official Warmflow service / installation manuals for each affected model.

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