High Lockout
F0 on Viessmann Vitodens 200-W

Your boiler has experienced a serious internal brain failure and the main control board likely needs to be replaced.

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 in fault position. Internal fault. Replace the control unit.

What causes this fault?

This fault occurs when the boiler's central processor can no longer communicate with the internal components or fails its own start-up safety checks. It is usually caused by an electrical component failure on the main circuit board or a surge that has damaged the delicate microchips that control the heating process.

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

F1View →F2View →F3View →

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 →