Viessmann No Power / Power Supply Failure

Unit will not start at all; no lights on indoor display

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Tripped circuit breaker, Blown internal fuse on indoor PCB, Faulty power supply section of indoor PCB, Loose wiring at terminal block

Safety: Use extreme caution when working with mains voltage. Turn off the breaker before opening covers.

Check breaker: Verify the dedicated AC breaker has not tripped. Reset if necessary and observe if it trips again.
Inspect indoor terminal block: Confirm L and N wires are tight and not burnt.
Check internal fuse: With power off, locate and test the fuse on the indoor PCB. Replace only with the same type and rating.
PCB replacement: If the fuse blows repeatedly or the board shows burn marks, the indoor PCB likely needs replacement.

Hard 4/5

Indoor Main Control PCB

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