Low
F1 on Atag S 25CR

Your boiler has detected that the concentration of chemical protector added to your heating system to prevent corrosion and freezing is outside of the recommended range.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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.

What the manual says

Manufacturer manual

Anti-freeze in combination with protector (Fernox F1 / Alphi 11)

From this model's manual
Verified against the Atag S 25cr installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

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

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