BoilerFaultCodesYour boiler has reached an unsafely high temperature and has shut down to prevent damage or overheating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Temperature safety sensor above 101 °C.
What causes this fault?
This fault occurs when the water inside the heat exchanger becomes too hot, causing the safety sensors to shut the system down to prevent damage. The most common reasons are a failed pump that isn't moving water away from the boiler quickly enough or a blockage in the pipework restricting flow. It can also be caused by a build-up of air or a faulty sensor sending an incorrect temperature reading to the control board.
This issue is more common during the first cold spell of autumn, when pumps that have been idle all summer can seize up or struggle to restart.
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 4F — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Ideal Maximiser SE 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.