On Neff heat pump dryers, E09 is displayed and the dryer does not heat; cycle runs with cool air only.

Safety first: Unplug the dryer. Heat pump systems contain high-voltage electronics and sealed refrigerant circuits; many repairs must be done by certified technicians.

User-level checks:

• Ensure all filters and the heat exchanger are completely clean to avoid false overheating conditions.
• Reset the appliance by disconnecting power for 5–10 minutes, then reconnect and try a short warm program.

Technical checks (for qualified personnel):

• Access the compressor and inverter module. Inspect for burnt components or loose connectors.
• Measure compressor winding resistances and check for shorts to earth.
• Verify supply voltage to the inverter and control signals from the main PCB.

If the compressor or sealed system is defective, the heat pump module usually must be replaced as a complete assembly. This is a complex repair and is generally not economical for DIY; contact an authorized Neff service partner.