nF1 High

Viessmann nF1 Fault Code

Also written as NF1 — same fault.

The Viessmann nF1 fault code means: your boiler has detected trapped air inside it which is preventing it from starting up safely.. It appears on 6 Viessmann 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: No air in the heat exchanger and the system prior to firing the appliance. This will cause nF1 fault and prevent you finishing the installation without hinderance.

What causes the Viessmann nF1 fault?

This fault occurs when air becomes trapped inside the main heat exchanger, preventing the boiler from successfully finishing its startup sequence. It is usually caused by a faulty automatic air vent or air that was not properly purged from the system after a refill or a repair.

This fault is most common in autumn when homeowners turn their heating back on for the first time or after radiators have been bled to prepare for winter.

Typical repair cost £80-160 (including labour)

DIY fix possible

Check that the radiator valves are open and the system is fully topped up with water to the correct pressure (usually 1.5 bar).Bleed all radiators in the house to remove any trapped air pockets.Restart the boiler to trigger the automatic venting program.

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Viessmann models that show the nF1 fault code

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

Source

Viessmann nF1 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026