E203
Navien
Zone Control / Internal Pump Control Fault
Navien furnace shows E203, unit does not respond to zone calls properly
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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
Incorrect wiring to external zone controller, Overloaded pump relay on PCB, Shorted pump wiring, Faulty internal pump driver
How to Fix / Troubleshooting
Safety: Turn off power before working on pump or control wiring.
- Review wiring diagram: Compare the actual wiring of external zone valves, pumps, and controllers to the Navien installation manual. Correct any miswiring.
- Inspect pump wiring: Check the internal primary pump and any external pump wiring for shorts to ground or between conductors. Repair damaged cables.
- Check pump load: Ensure that the pump connected to the Navien's pump output does not exceed the rated amperage. Oversized pumps can damage the PCB relay.
- Test pump operation: With power restored briefly, call for heat and verify that the pump starts and runs smoothly. If the pump is seized or noisy, replace it.
- PCB evaluation: If wiring and pumps are correct but E203 persists, the internal pump driver or relay on the PCB may be damaged and require board replacement by a technician.
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Repair Difficulty
Hard
4/5
Required Part
Internal Pump Relay on PCB
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