P0
Vaillant
Inverter Module Protection / DC Bus Voltage Fault
P0 code, unit does not start compressor, only fan may run
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Safety Warning
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.
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Possible Causes
Abnormal DC bus voltage on inverter PCB, Faulty PFC circuit, Loose DC bus connectors, Shorted IGBT module
How to Fix / Troubleshooting
Safety: The inverter board contains high‑voltage capacitors that can retain charge after power off. Only trained personnel should service this area.
- Power reset: Turn off power at the breaker and outdoor isolator for at least 10 minutes to allow capacitors to discharge. Restore power and test.
- Inspect wiring: With power off, check all plug‑in connectors on the outdoor PCB for secure fit. Look for burn marks or melted plastic.
- Check for contamination: Remove dust and insect nests from the control box using a dry brush and vacuum.
- Do not bypass protections: Never attempt to jumper or bypass inverter protections.
- Professional repair: P0 usually indicates a failed inverter power module or related circuitry. Replacement of the outdoor PCB should be done by an authorized Vaillant technician.
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Repair Difficulty
Professional Required
5/5
Required Part
Outdoor Inverter Power Module / PCB
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