High Lockout
F7 on Viessmann Vitodens 333

Your boiler has shut down because it is unable to accurately measure the air pressure required for its burner to operate safely.

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 blocked. Differential pressure sensor faulty. Cause: Check the differential pressure sensor and lead.

What causes this fault?

This fault occurs when the boiler's internal computer receives an incorrect or missing signal from the sensor that monitors air flow. The most common cause is a physical blockage in the burner or a failure in the electronic sensor that ensures the unit is breathing correctly for safe 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.

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Related fault codes

F8View →F9View →

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