BoilerFaultCodesYour boiler has overheated to a critical level and a safety component has permanently cut the power to prevent serious damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: THERMAL FUSE LOCKOUT
What causes this fault?
This fault occurs when the internal temperature inside the main heat exchanger has reached an extreme, dangerous limit, causing a one-time safety fuse to blow. The root cause is typically a severe lack of water flow or a significant build-up of debris and limescale that has caused the component to dry-fire and get too hot. Because the fuse is designed to break permanently to protect your home, the boiler cannot be restarted simply by pressing a button.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like 4.5 — 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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