BoilerFaultCodesTechnical description
If the unit continues to trip then the flue should be checked for spillage.
What causes this fault?
This fault occurs when a safety sensor detects that the hot exhaust gases are not rising correctly through the chimney and are instead spilling back into the room. The most common reason is a blockage in the flue, a damaged chimney liner, or poor atmospheric conditions that prevent the natural pull of the chimney. Because these fumes contain carbon monoxide, the boiler shuts down immediately to prevent a dangerous build-up in your home.
This issue is more common during particularly windy weather or high-pressure summer days when atmospheric conditions can push air back down the chimney, causing a 'down-draught'.
Engineer required
This is a emergency severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.