290
Moderate
Lennox · HVAC Systems (AC, Furnaces & Heat Pumps)
Indoor Coil Thermistor Fault
Quick Answer
Error code 290 on your Lennox HVAC Systems (AC, Furnaces & Heat Pumps) means: Indoor Coil Thermistor Fault. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
Likely Causes
How to Fix It
1
Locate the indoor coil thermistor and check its connector for firm seating
2
Measure the thermistor resistance with a multimeter and compare to the resistance/temperature chart
3
Inspect the wiring from the sensor to the control board for breaks or damage
4
Verify the sensor is properly mounted to the evaporator coil surface
5
Replace the sensor if resistance is out of the expected range
Pro Tip
This fix requires some technical knowledge. If you're unsure about any step, consider contacting support or a qualified technician.
Parts You May Need
Indoor coil thermistor
Wire connectors
Sensor mounting clip
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