Emerson Thermostat Calling but Equipment Not Responding

Thermostat shows "Heat On" or "Cool On" but equipment does not start

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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

Open circuit between thermostat and control board, Blown low-voltage fuse, Failed furnace/air handler control board, Safety lockout on equipment

How to Fix / Troubleshooting

Safety first: Turn off power to the furnace/air handler and outdoor unit at the breakers before opening panels.

Steps to troubleshoot:

  • 1. Confirm call: Verify the Emerson thermostat indicates a call for heat or cool (e.g., "Heat On" icon).
  • 2. Inspect control board fuse: At the furnace/air handler, check the low-voltage fuse and replace if blown.
  • 3. Check wiring continuity: Ensure the thermostat wires are firmly connected at both ends and not damaged.
  • 4. Look for error lights on equipment: Many furnaces and outdoor units have diagnostic LEDs. Note any blink codes and refer to the equipment manual.
  • 5. Test with jumper (advanced): With thermostat removed and power on, jumper R to W (heat) or R to Y (cool) at the furnace board. If the equipment still does not start, the issue is in the equipment, not the thermostat.

When to call a professional: Equipment lockouts, control board failures, and safety switch issues should be diagnosed by an HVAC technician.

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Repair Difficulty

Hard 4/5

Required Part

Furnace/Air Handler Control Board
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