BoilerFaultCodesYour boiler has detected that the gas supply is not shutting off as quickly as it should, preventing the system from firing up safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Fuel valve closes too late
What causes this fault?
This fault occurs when the boiler's internal safety checks detect that the gas valve is failing to shut off the fuel supply immediately after a heating cycle. The most common reason is a mechanical failure within the gas valve itself or a faulty sensor on the control board providing incorrect signals. Because the system cannot guarantee the gas flow will stop when required, it prevents the boiler from starting as a critical safety precaution.
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 F8 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Viessmann Vitodens 100 Compact 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.