BoilerFaultCodesYour boiler has paused its initial setup process because the automatic air-venting sequence has not finished successfully.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Installation in unfinished state - Fault during boiler venting
What causes this fault?
This fault occurs during the commissioning stage when the boiler's internal computer determines that air is still trapped within the heat exchanger or primary circuit. It is often triggered because the automatic venting program was interrupted or the system's air bleed valve is stuck, preventing the unit from safely transitioning into normal operation. No gas will be ignited until the boiler is satisfied that all air has been purged to prevent overheating.
DIY fix possible
Check that the manual air vent on top of the boiler is openEnsure the central heating system pressure is between 1.0 and 1.5 barPress and hold the 'Mode' or 'Reset' button to restart the commissioning sequence
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 b0 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Viessmann Vitodens Tec is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.