BoilerFaultCodesYour boiler has detected an electrical fault with one of its main internal temperature sensors, causing the system to shut down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Safety sensor short-circuited.
What causes this fault?
This fault occurs when the boiler's safety sensor, which monitors for overheating, sends an abnormal electrical signal to the control board. The most common reason is that the sensor's internal wiring has failed or a moisture leak has caused a short circuit. Because this sensor is responsible for preventing the boiler from becoming dangerously hot, the system will not start until the part is replaced.
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 4L — 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.