BoilerFaultCodesYour boiler has stopped working because the fan cannot properly push exhaust fumes out or pull fresh air in through the flue pipe.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Air intake/flue blocked
What causes this fault?
This fault occurs when the boiler's internal safety sensors detect that the fan is not moving air through the system at the required speed. The most common reasons are a physical blockage in the flue pipe outside, a build-up of debris within the fan itself, or a failure in the electronic sensor that monitors air pressure.
This issue is more frequent during periods of high winds or extreme cold, as gales can disrupt the airflow through the flue and heavy snow can physically block the air intake.
DIY fix possible
Check the external flue pipe for obvious visual obstructions like bird nests, leaves, or debrisEnsure the external flue terminal is not covered by garden furniture or building materialsGently clear any visible snow or ice buildup from the flue outlet
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A boiler cover plan would cover faults like C6 — no call-out fees, no surprises.
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Worcester Bosch Greenstar Utility 18/25 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.
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