BoilerFaultCodesYour boiler has detected that a safety sensor in the flue pipe is reporting an incorrect temperature reading.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: FLUE THERMISTOR ERROR
What causes this fault?
This fault occurs when the boiler's control board receives an impractical temperature reading from the sensor located in the exhaust flue. It usually happens because the sensor has failed internally or the electrical wiring connecting it to the main board has become damaged or loose. Because this sensor is a critical safety component designed to prevent the boiler from overheating, the system will shut down immediately to prevent damage.
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 H.....4...... — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Ideal Mexico HE 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.