Carrier
No Call for Heat Reaching Furnace
Thermostat calls for heat but Carrier furnace does not respond; LED shows normal idle, no fault codes.
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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
Broken thermostat wire on W circuit, miswired thermostat, failed thermostat, open float switch in condensate line
How to Fix / Troubleshooting
Safety first: Turn off power before handling low-voltage wiring.
- Verify thermostat operation: Replace thermostat batteries if present. Set mode to HEAT and raise setpoint.
- Check W signal at furnace: At the Carrier control board, with power on and a call for heat, measure between W and C (or use a simple test light). If no 24V is present, the issue is between thermostat and furnace.
- Inspect thermostat cable: Look for breaks or damage along the thermostat wire path.
- Check condensate safety switch: Some installations route the W signal through a float switch on the condensate pump or drain pan. If the pan is full or the switch is open, the furnace will not receive the call for heat.
If wiring and safety switches are intact, replacing the thermostat may resolve the issue.
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Repair Difficulty
Medium
3/5
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