BoilerFaultCodesTechnical description
Response from accessory module or defective condensate pump is blocking burner operation
What causes this fault?
This fault occurs when a mechanical flap inside the exhaust system fails to open, which safely prevents outdoor air or fumes from flowing back into the boiler. The most common cause is the flap becoming physically stuck due to a build-up of debris or the fan failing to generate enough pressure to push it open.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register →