High Lockout
FE on Viessmann Vitodens 100-W / 200-W

Your boiler's internal computer has encountered a critical error or is having trouble communicating with its electronic security card, causing the system to shut down for safety.

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. Strong interference (EMC) field nearby; alternatively boiler coding card or main PCB faulty. Remove EMC interference. If the equipment will not restart, check the boiler coding card and replace, or replace the control unit.

What causes this fault?

This fault occurs when the boiler's main control board loses its connection with the small electronic chip that tells it how to operate safely. It is usually caused by electrical interference, a loose chip connection, or a physical failure within the central circuit board itself. Because the boiler no longer knows its own safety parameters, it shuts down immediately to prevent damage.

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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