E4
Vaillant
Discharge Temperature High Protection
E4 error, compressor stops, 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 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 bent fins with a fin comb.
- Verify outdoor fan: Confirm the fan starts immediately with the compressor and runs at full speed. Replace the fan motor or capacitor if not.
- Check ambient conditions: In very high outdoor temperatures, ensure the unit has adequate shade and airflow.
- Reset and test: After cleaning and verifying fan operation, reset power and test again.
- If E4 persists: The discharge sensor or refrigerant circuit may be at fault. A Vaillant technician should check 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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