BoilerFaultCodesWhat the manual says
Manufacturer manualFlow sensor open circuit. Check cable/connections not damaged. Renew sensor/cable. Check connections on control
What causes this fault?
This fault occurs when the boiler's control system fails to detect a consistent flame after several ignition attempts, causing it to shut down for safety. The most common reasons are a worn-out sensing probe that can no longer 'see' the flame, or a blockage in the internal drainage system that causes water to back up into the burner.
This issue is more frequent during very cold spells, as frozen external drainage pipes can prevent the boiler from clearing waste water, leading to a flame failure.
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 E04: no call-out fees, no surprise bills.
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