BoilerFaultCodesYour boiler thinks it sees a flame even though it hasn't turned the gas on, which is often caused by a faulty sensor or moisture in the system.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flame detected when the gas valve should be closed.
What causes this fault?
This fault occurs when the boiler's internal computer wrongly detects a flame signal before the ignition sequence has even started. It is usually caused by a dirty or corroded sensor that is sending a false electrical signal, or moisture within the wiring creates a short circuit that mimics a flame.
This issue can be more frequent during periods of high humidity or heavy rain, as internal dampness or moisture ingress can interfere with the sensitive electrical flame signals.
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 6C — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Worcester Bosch Highflow 400 BF 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.