High Lockout
E08 on Viessmann Vitodens 100-W

Your boiler is unable to light because the internal fan is spinning too quickly for the system to safely start the ignition process.

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

Burner does not start. Fan speed too high during burner start.

What causes this fault?

This fault occurs when the boiler's control system detects that the internal fan is spinning faster than the required safety limit during the start-up sequence. The most common reason is a communication error between the fan and the main circuit board, or a failure in the fan's internal speed sensor. Because the boiler cannot accurately control the air-to-gas ratio, it shuts down for safety reasons.

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

F4View →B1View →

Related guides you might find useful

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →