BoilerFaultCodesYour boiler has detected a fault with the sensor that monitors exhaust gases, and as a safety precaution, it will not operate until this is fixed.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flue sensor damaged
What causes this fault?
This fault occurs when the internal sensor responsible for monitoring the temperature of the exhaust gases becomes faulty or disconnected. The most common reason is natural wear and tear or heat damage to the sensor's thermistor, which prevents it from sending an accurate reading to the main control board. As a safety measure, the boiler shuts down to prevent any risk of the flue system overheating.
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 E23 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Ravenheat CS 80/90, WH System, WH 80/90 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.