Vaillant Transformer 5-8kW 1P 0020175833

The Vaillant 0020175833 is a single-phase transformer rated for 5-8 kW appliances, used in the Arotherm VWL 85/2 A 230V heat pump family. It supplies the low-voltage rail that the appliance's control and power electronics run from. It is a serviceable component mounted inside the unit.

• The appliance does not power up or the display stays dead with mains present.
• Repeated blowing of the transformer's protective fuse on the primary side.
• Control board receives no low-voltage supply, so no fault codes or status LEDs appear.
• Intermittent shutdowns or erratic control behaviour that trace back to an unstable low-voltage rail.
• Visible overheating, discolouration or burning smell around the transformer windings.

• Confirm the appliance model and serial number against the manufacturer's parts list.
• Check the rating matches the 5-8 kW, single-phase specification of the failed unit.
• Verify the fault is at the transformer and not upstream at the supply, fuse or PCB.
• Isolate the electrical supply and follow the manufacturer's safety guidance before fitting.