BoilerFaultCodesYour boiler has detected that the exhaust gases are becoming too hot and has shut down as a safety precaution.
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 overheating
What causes this fault?
This fault occurs when the internal temperature of the exhaust pipe exceeds safe limits, triggering an emergency shutdown to prevent damage to the plastic flue components. The most common reason is a buildup of limescale or debris inside the heat exchanger, which prevents heat from being transferred to the water and sends it out through the chimney instead. In some cases, it can also be caused by a faulty sensor sending an incorrect high-temperature reading to the main control board.
This fault often becomes more apparent during winter when the boiler is running at maximum capacity for long periods to heat a cold home.
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 22E — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Ravenheat HE 80/90 / HE 25-30s / HE 80-98s / HE 8-98s / HE 25-30s compact 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.