Vaillant Inverter 0020266449

The Vaillant 0020266449 is an inverter module used in Vaillant Arotherm 5/5 air source heat pump outdoor units. It controls the speed of the compressor motor by varying the electrical supply frequency, allowing the heat pump to modulate its output rather than running only at fixed speed. It is a serviceable electronic component within the outdoor unit.

• The outdoor unit fails to start or the compressor does not run.
• The heat pump repeatedly trips, locks out, or reports an inverter or compressor-related fault at the controller.
• Output is lost or the unit runs only intermittently despite a valid heating or hot water demand.
• Audible humming or buzzing from the outdoor unit without the compressor starting.
• Visible damage, burning or discolouration on the inverter module itself.

• Confirm the model and serial number of the outdoor unit against the manufacturer's parts list.
• Check that the existing inverter carries the part number 0020266449.
• Verify the fault has been correctly diagnosed as an inverter failure rather than a supply, sensor or compressor fault.
• Installation involves work on the refrigerant circuit and mains electrical supply, so it should be carried out by a competent heating engineer.