BoilerFaultCodesYour boiler is struggling to keep a steady flame lit, causing it 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: Unstable flame (analogue input), underfloor heating contact or gas valve fault
What causes this fault?
This fault occurs when the boiler's control board detects that the flame is flickering or unstable, making it unsafe to continue running. The most common reasons are a buildup of carbon on the sensing probes or a failing gas valve that isn't providing a steady flow of fuel to the burner.
This fault can be more frequent during the first cold snap of winter when the boiler is suddenly forced to run at maximum output for long periods, putting strain on aging gas components.
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.88 — no call-out fees, no surprises.
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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.
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