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  1. B

    Viessmann Vitodens 100 - Control Unit?

    Apologies for resurrecting this thread but I've just had the F4 issue intermittently on a WB1A and fixed it without replacing the main board. It turned out, for me at least, that replacing a single inexpensive transistor was all that was required. As others have said, the voltage to the...
  2. Untitled

    Untitled

  3. WB1A

    WB1A

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