E4
Viessmann
Low Voltage / Power Supply Fault
Display shows E4 and unit reports power supply error
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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
Defective external power adapter, Loose power connector, Internal power supply failure on control board, Incorrect mains voltage
How to Fix / Troubleshooting
Safety first: Disconnect the unit from mains before inspecting power components.
- Check mains outlet: Verify that the outlet provides the correct voltage using a suitable tester.
- Inspect power adapter: If your Viessmann softener uses an external adapter, check for damage, overheating, or loose plugs. Replace with an original-rated adapter if suspect.
- Examine power connector: Ensure the low-voltage connector is firmly plugged into the control board.
- Power cycle: Reconnect and see if E4 clears. If the error persists and the adapter is known good, the internal power supply on the control board may be faulty.
- Board replacement: Replace the Viessmann control board if internal power circuits are defective.
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Repair Difficulty
Medium
3/5
Required Part
Viessmann Power Adapter
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