BoilerFaultCodesYour boiler is struggling to breathe properly because the exhaust pipe outside might be blocked or the gas is not burning correctly, causing the system to shut down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Poor combustion – flue terminal may be blocked
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the gas isn't burning cleanly or safely. The most common reason is a physical obstruction in the flue pipe outside, but it can also be caused by an incorrect mixture of gas and air during the ignition process. To protect you from carbon monoxide, the system automatically shuts down when it detects these poor combustion levels.
This fault is more common during autumn and winter, as fallen leaves or heavy snow can easily block the external flue terminal.
DIY fix possible
Check the external flue terminal (the exhaust pipe on your outside wall) for obstructions like bird nests, leaves, or debris.Carefully remove any visible blockages from the end of the pipe.Reset the boiler by turning the selector switch to 'R' for at least five seconds.
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 E53 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Baxi GA Range 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.