E17
Carrier
Second-Stage Control Fault
Thermostat displays E17 and may not control second-stage heating or cooling; system may struggle to reach setpoint.
Advertisements
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.
Advertisements
Possible Causes
Open or miswired Y2 or W2 terminal, Failed second-stage relay on Carrier control board, Incorrect staging configuration in thermostat, Broken thermostat conductor for second stage
How to Fix / Troubleshooting
Safety first: Turn off power to the HVAC system at the breaker before working on wiring.
- Step 1 – Verify staging settings: In the thermostat installer menu, confirm the correct number of heating and cooling stages is selected for your Carrier equipment.
- Step 2 – Inspect Y2/W2 wiring: At the thermostat and control board, ensure Y2 and/or W2 wires are connected and secure. Tighten any loose terminals.
- Step 3 – Continuity test (advanced): With power off and wires disconnected, test continuity of the Y2/W2 conductors between thermostat and control board. Replace cable if open.
- Step 4 – System test: Use the thermostat's system test mode to energize second-stage outputs and verify that the furnace or condenser responds.
- Step 5 – Replace control board if needed: If the thermostat is sending a proper call but the board does not energize second stage, the board's stage relay may be failed.
- When to call a pro: Staging affects comfort and efficiency; a Carrier technician should verify proper operation after repairs.
Advertisements
Repair Difficulty
Medium
3/5
Required Part
Carrier Furnace/Air Handler Control Board
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements