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F.404

F.404 — Burner in fault state due to control unit error

Viessmann · Vitodens 100-W Boiler

What does F.404 mean?

The burner is in a fault state because the BCU burner control unit is faulty. This error prevents the boiler from starting or operating.

Common Causes

  • BCU burner control unit is faulty

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Reset the boiler by briefly turning off and on its power supply.

  2. 2

    If the fault recurs immediately, contact a qualified heating engineer.

  3. 3

    An engineer will need to replace the BCU burner control unit.

Browse all codes in this manual (60)
Verified technical data. Last updated: April 2026

Related Faults

Connection errorConnection error — Displayed on programming unitF.142F.142 — Burner in fault state due to CAN bus communication errorF.160F.160 — Burner in fault state due to CAN bus communication error
Source: Viessmann Vitodens 100-W Boiler
Open Manual (Page 79)Search more codes in this manual