BoilerFaultCodesWhat the manual says
Manufacturer manualToo much resistance or dirt in the air circuit; check the air supply/combustion gas discharge system, the burner, and the heat exchanger.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that air cannot flow freely through the system to support safe combustion. The most common reason is a buildup of debris or soot within the heat exchanger or burner, which physically restricts the path of the gases. It can also be caused by an external blockage in the flue pipe or a failing fan that is unable to push air through the circuit effectively.
This fault often appears during the first heavy use of autumn or winter, as dust or debris settled during the summer months can be pulled into the burner when the heating starts running at full power.
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.
Avoid the next call-out bill
A cover plan would handle faults like 18: no call-out fees, no surprise bills.
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