High Lockout
24 on Ideal Maximiser SE

Your boiler has lost communication with one of its internal sensors, meaning it cannot accurately monitor temperatures to run safely.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Sensor defect or improper contacts and connections.

What causes this fault?

This fault occurs when the boiler's control board can no longer read the temperature signals from the internal sensors. The most common reason is a physical failure of the thermistor component itself, or loose wiring connections caused by the natural vibrations of the boiler over time.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related guides you might find useful

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →