High Lockout
431 on Ideal Ideal Classic SE15P FF

Your boiler has detected a fault with its temperature sensor, which means the system cannot safely monitor the heat of the water and has stopped working as a precaution.

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

NTC1 short circuit

What causes this fault?

This fault occurs when the boiler's main internal temperature sensor develops an electrical short, preventing it from reading how hot the water is. The most common reason is that the sensor itself has failed internally, or moisture has compromised the electrical connections between the sensor and the main control board.

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 fault codes

4 30View →4 32View →

Related guides you might find useful

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →