BoilerFaultCodesYour boiler's safety system is detecting a flame when there shouldn't be one, or the sensor that monitors the flame has developed a fault.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Incorrect sensing of flame
What causes this fault?
This fault occurs when the boiler's internal computer detects an electrical signal signifying a flame even though the gas valve should be closed. The most common reasons are a moisture-damaged ignition lead causing a short circuit, a gas valve that is leaking slightly, or a faulty sensor that is incorrectly reporting a flame to the control board.
This fault can sometimes appear after periods of heavy rain or high humidity, as moisture ingress into the casing can interfere with the sensitive electrical signals of the flame sensor.
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 F.27 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
Affiliate links — we may earn a commission at no extra cost to you.