BoilerFaultCodesYour boiler is struggling to light or keep a flame burning correctly because the gas and air mixture isn't balanced.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flame detection and mixture
What causes this fault?
This fault occurs when the boiler's internal sensor fails to detect a consistent flame after it tries to ignite. The root cause is usually a breakdown in the balance between gas and air, or a worn-out sensor that can no longer tell the control board that the fire is safely lit.
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 85 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Ideal Response 80 100 120 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.