BoilerFaultCodesYour boiler has shut down because a safety sensor has detected that dangerous exhaust fumes are not escaping through the chimney correctly.
Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now — this fault can be dangerous if ignored.
Technical description: The Products Discharge Safety Device (TTB) has operated in the case of flue blockage and the boiler has gone to lockout.
What causes this fault?
This fault occurs when a safety sensor detects that combustion gases are blowing back into the room instead of escaping through the chimney. The most common reasons are a blockage in the chimney, such as a bird's nest or debris, or severe atmospheric conditions preventing the natural flow of exhaust. The boiler shuts down immediately to prevent harmful carbon monoxide from entering your home.
This fault is more frequent during periods of high winds or extreme cold, which can create pressure imbalances or 'downdraughts' in the chimney flue.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like Red LED illuminated (Lockout) — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Potterton Kingfisher MF RSL is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.