Your boiler has detected an issue with how air is moving through the system, preventing it from lighting safely to provide heating or hot water.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Electrical/pressure tube connections, blockage of pressure tubes, restriction in flue, or venturi issue (Section E)
What causes this fault?
This fault occurs when the boiler's internal fan fails to create the specific air pressure needed to prove it is safe to ignite. The most common reasons are a build-up of dirt in the small 'venturi' tube, a failing fan motor, or a blockage in the flue pipe that prevents waste gases from escaping properly.
This issue is more frequent during periods of heavy rain or high winds, which can sometimes cause debris to enter the flue or create pressure fluctuations that trigger the sensitive switch.
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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