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Connection error

Connection error — Displayed on programming unit

Viessmann · Vitodens 100-W Boiler

What does Connection error mean?

A 'Connection error' appears on the display unit, indicating a problem with the communication between the heat management unit and the programming unit.

Common Causes

  • Faulty connecting cable between HMU heat management unit and HMI programming unit
  • Loose plug between HMU heat management unit and HMI programming unit

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Check the connecting cable between the HMU heat management unit and the HMI programming unit for any visible damage.

  2. 2

    Ensure that the plug connecting these units is firmly and correctly seated.

  3. 3

    Reset the boiler's power supply to attempt to re-establish the connection.

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

Related Faults

F.142F.142 — Burner in fault state due to CAN bus communication errorF.160F.160 — Burner in fault state due to CAN bus communication errorF.161F.161 — Burner in fault state due to BCU data memory access error
Source: Viessmann Vitodens 100-W Boiler
Open Manual (Page 69)Search more codes in this manual