E4
Vaillant
Discharge Temperature High Protection
E4 error: The compressor stops, and the unit may blow warm air in cooling mode.
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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
Blocked outdoor coil, Outdoor fan failure, Low refrigerant flow due to a restriction, Overcharge or non-condensables, Faulty discharge temperature sensor
How to Fix / Troubleshooting
Safety: Isolate power before cleaning or inspection. The discharge line can be very hot.
- Clean outdoor coil: Remove debris and wash the coil with low-pressure water. Straighten any bent fins with a fin comb.
- Verify outdoor fan: Confirm that the fan starts immediately with the compressor and runs at full speed. Replace the fan motor or capacitor if it does not.
- Check ambient conditions: In very high outdoor temperatures, ensure the unit has adequate shade and and sufficient airflow.
- Reset and test: After cleaning and verifying fan operation, reset power and test the unit again.
- If E4 persists: The discharge sensor or refrigerant circuit may be at fault. A Vaillant technician should check the discharge temperature, sensor resistance, and system pressures.
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Repair Difficulty
Hard
4/5
Required Part
Discharge Pipe NTC Temperature Sensor
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