Technical description
Goes off during an ignition trial period.
What causes this fault?
This fault occurs when the boiler's control system fails to detect a stable flame after it attempts to light. The most common reason is a coating of carbon or dirt on the sensing probe which prevents it from 'seeing' the fire, or a restriction in the gas supply preventing a strong enough flame from forming.
This issue can be more frequent during the first cold snap of autumn when debris has settled on the electrodes after a summer of inactivity.
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.