BoilerFaultCodesYour boiler has detected a blockage or debris in its exhaust system which is preventing waste gases from being safely removed.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Debris in flue system; Debris in flue venturi. Appears if the boiler or flue system has developed a fault.
What causes this fault?
This fault occurs when the boiler's internal safety sensors detect that the airflow through the exhaust pipe is restricted or blocked. The most common cause is a build-up of dirt within a small component called the venturi, or a mechanical failure in the fan that prevents harmful waste gases from being pushed out of the property.
This fault can be more frequent during autumn and winter, as high winds can blow external debris into the flue or cause pressure shifts that trigger the safety sensor.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like 03 — no call-out fees, no surprises.
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