High Lockout
29 on Intergas Rapid 25

Your boiler's fan is failing to maintain a steady speed, which prevents the system from safely drawing in air and exhausting gases.

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

Fan speed varies

What causes this fault?

This fault occurs when the boiler's internal computer detects that the fan is spinning at an inconsistent or incorrect speed to safely clear exhaust gases. The most common reason is a mechanical failure within the fan motor or a communication error caused by damaged wiring or a faulty control board. Without a steady and predictable airflow, the boiler shuts down as a safety precaution to prevent improper combustion.

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

24View →

Related guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

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 →