E17
iComfort
Equipment Interface Module Communication Failure
Thermostat displays E17 and reports equipment interface module not detected
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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
No power to equipment interface module, Open communication cable between thermostat and interface, Miswired interface terminals, Failed interface module electronics
How to Fix / Troubleshooting
Safety first: Turn off power to all HVAC components and the equipment interface module before opening any covers.
- Step 1 – Verify power to interface: Check that the equipment interface module has 24 VAC between its R and C terminals. If not, trace back to the indoor unit transformer and fuse.
- Step 2 – Inspect communication wiring: Confirm that the communication pair from the thermostat is correctly landed on the interface module’s designated terminals and that polarity is consistent.
- Step 3 – Check status LEDs: Many interface modules have status LEDs. Refer to the manual to interpret LED patterns and identify power or communication issues.
- Step 4 – Bypass interface (if possible): For testing, connect the thermostat directly to the indoor unit (if supported) to see if E17 clears. This helps confirm a faulty interface module.
- Step 5 – Replace interface module: If wiring and power are correct and E17 persists, replace the iComfort equipment interface module with an identical model.
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Repair Difficulty
Hard
4/5
Required Part
iComfort Equipment Interface Module
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