Viessmann Low Voltage Protection

System stops; P1 error; may be intermittent with power fluctuations

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

Undersized supply wiring, Voltage drop due to long cable runs, Utility supply issues, Loose terminals at breaker or isolator

Safety: Turn off power before tightening any electrical connections.

Measure voltage under load: Use a multimeter to check voltage at the outdoor unit while the system attempts to start.
Inspect wiring size: Ensure the cable gauge meets Viessmann installation requirements.
Tighten terminals: Check and tighten all connections at the main panel, isolator, and outdoor unit.
Consult electrician: If low voltage persists, an electrician should correct the supply issue.

Hard 4/5