E3
Vaillant
Low‑Pressure Protection / Refrigerant Undercharge
E3 error, compressor stops shortly after starting, poor cooling
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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
Refrigerant leak in indoor or outdoor coil or piping, Blocked expansion device, Severely clogged indoor filter or coil, Faulty low‑pressure switch or sensor
How to Fix / Troubleshooting
Safety: Refrigerant is under high pressure and can cause injury. Only certified personnel should connect gauges or open the circuit.
- Check filters and coils: Clean indoor filters and inspect both indoor and outdoor coils for heavy dirt buildup. Clean as needed.
- Inspect for oil stains: Look along refrigerant pipes, flare joints, and coils for oily residue, which indicates a leak. Do not tighten flares while the system is pressurized.
- Power reset: After cleaning, power cycle the unit and test operation. If E3 returns, do not continue to run the system.
- Professional service: A Vaillant technician should perform leak detection, repair any leaks, evacuate, and recharge the system to the specified amount. The low‑pressure switch or sensor should also be tested.
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Repair Difficulty
Professional Required
5/5
Required Part
Low‑Pressure Switch / Sensor
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