BoilerFaultCodesYour boiler has shut down because the internal gases leaving the system have become too hot, triggering a safety switch to protect the plastic exhaust pipe from melting.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The flue gas thermostat will operate to protect the plastic flue system from high temperatures.
What causes this fault?
This fault occurs when the heat exchanger is unable to transfer heat effectively into the water, causing intense heat to escape into the plastic exhaust pipe instead. The most common reasons are a build-up of debris inside the main heat exchanger or a lack of water flow, which forces the safety switch to trip to prevent the flue from melting.
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 Flue Gas Thermostat Reset Button — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Worcester Bosch Greenstar HE 12/22 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.