E5
Vaillant
Overcurrent / Compressor Overload Protection
E5 error, compressor does not start or stops quickly, humming noise from outdoor unit
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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
Shorted or locked compressor, Incorrect supply voltage, Loose power connections, Faulty inverter module (on inverter models), Blocked outdoor fan causing high current
How to Fix / Troubleshooting
Safety: High voltage is present in the outdoor unit. Only qualified persons should work inside the control box. Always isolate power first.
- Check supply voltage: Verify that the mains voltage matches the rating on the Vaillant nameplate. Undervoltage or overvoltage can trigger E5.
- Inspect terminals: With power off, tighten all main power terminals in the outdoor unit and at the isolator. Look for signs of overheating or melted insulation.
- Verify outdoor fan: Ensure the fan runs freely and is not stalled, which can increase compressor load.
- Power cycle: Restore power and test. If E5 recurs immediately with a loud hum and no compressor start, the compressor or inverter is likely faulty.
- Professional diagnosis: Measuring compressor winding resistance, insulation, and inverter output requires specialist tools. Contact a Vaillant service center for further testing and possible replacement of the compressor or inverter PCB.
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Repair Difficulty
Professional Required
5/5
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