High Lockout
E4 on Viessmann Vitodens 333

Your boiler has stopped working because it is not receiving the correct electrical supply, preventing the burner from igniting.

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

Fault - supply voltage. Burner blocked

What causes this fault?

This fault occurs when the boiler's internal control system detects an issue with the electrical power reaching the burner components. The most common reason is a failure in the ignition transformer or the main control board, which prevents the boiler from creating a spark to light the gas. It can also be triggered by loose internal wiring or fluctuations in your home's mains electricity supply.

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.

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Related fault codes

E5View →F4View →

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