BoilerFaultCodesYour boiler has detected trapped air inside it which is preventing it from starting up safely.
Book a Gas Safe engineer within 24–48 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 this 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.
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.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like nF1 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
Affiliate links — we may earn a commission at no extra cost to you.