Heat Pump Troubleshooting
Before you call the repairman, try this basic heat pump troubleshooting guide. This guide will help you to diagnose problems with your typical residential ducted heat pump system.
Visual & Step-by-Step Diagnosis
Understanding heat pump operation is critical for proper diagnostics. In the video accompanying this guide, I walk through the 2026 checklist for a system that isn't heating or cooling effectively.
- Pro Tip: Watch the outdoor fan behavior in the video to see if your defrost cycle is engaging correctly.
- Safety First: Always disconnect high-voltage power before removing any service panels.
At the Thermostat
**NOTE** ONLY YOU CAN ASSESS YOUR ABILITY TO PERFORM THIS TASK. THIS IS A GUIDE AND CANNOT PROVIDE ALL OF THE DETAILS FOR EVERY SITUATION.
Begin your heat pump troubleshooting at the thermostat by ensuring it is on the correct mode (Heat or Cool) and that it is set higher or lower than the actual room temperature. This ensures there really is a demand for the system to run.
Is there air coming out of the registers?
If there is no air movement, check to see if the outdoor unit is running. If neither the indoor blower nor the outdoor unit is running, check the breakers for the furnace/air handler and the heat pump.
If the breaker is not tripped, the problem may be your thermostat, the furnace/air handler control board, or the low-voltage control wires.
If you have a condensate pump, check if the reservoir is full. A full reservoir will trip a safety switch, stopping the system.
If the indoor blower is running but the outdoor unit is not, continue your troubleshooting at the outdoor condensing unit.
Is the Outdoor Unit Running?
If the outdoor fan is not running, shut the power off to the unit. Check all wire connections for signs of burning or damage. Use a voltmeter to verify you have 240V at the unit and 24V at the contactor coil.
If the compressor starts but the fan does not, the outdoor fan motor or its run capacitor could be failed. If the fan starts but the compressor does not, the unit may be low on refrigerant or have a bad compressor.
Ice Build-up and Defrost Issues
In winter, a light coating of frost is normal. If you see the unit is encased in thick ice, turn the system to "Emergency Heat" to stop the outdoor unit and allow it to thaw using the indoor electric strips.
Thick ice usually points to a failure of the defrost control board, the outdoor fan motor, or a refrigerant charge issue.
Frequently Asked Questions
Why is my heat pump blowing steam or smoke in the winter?
This is the defrost cycle. To melt ice on the outdoor coil, the unit reverses its operation. The resulting water vapor looks like smoke. As long as it stops after 10-15 minutes, your system is working perfectly.
Why is my electric bill so high when using my heat pump?
If your heat pump isn't working efficiently, your thermostat will engage Auxiliary (Electric) Heat. These heat strips consume roughly three times more electricity than the heat pump itself.
How do I know if my reversing valve is bad?
If your system only cools or only heats regardless of the thermostat setting, the reversing valve solenoid may have failed or the internal slide is stuck.
Identify the Failing Component
If your troubleshooting has led you to a specific part, use these expert guides to test and replace the component safely:
Compressor
The heart of your system. Learn how to identify mechanical failure versus electrical issues.
Diagnose Compressor →Refrigerant Levels
Low charge causes icing and high bills. Understand how to check for leaks and proper levels.
Check Charge →Contactor
The high-voltage switch for your outdoor unit. Learn to check for pitted points or a burnt coil.
Test Contactor →Outdoor Fan
If the fan isn't spinning, the system will overheat or ice up. Test the motor and blades.
Fix Outdoor Fan →Control Board
The brain of the indoor or outdoor unit. Look for diagnostic flash codes and burnt traces.
Replace Board →Blower Motor
No airflow inside? The blower motor or its capacitor is likely the culprit.
Check Blower →Capacitors
The #1 failure in HVAC. Learn to safely discharge and test Microfarads (MFD).
Test Capacitors →Thermostat
Ensure your thermostat is sending the correct signals to the furnace and heat pump.
Thermostat Help →Amazon Store
Find the exact tools and replacement parts I use in my field-tested repair videos.
Shop Parts →YouTube Channel
Watch over 100+ DIY repair videos and live troubleshooting walkthroughs.
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Meet the Expert: HVAC Repair Guy (Richard Reed)
HVAC Specialist & Founder of HVAC For Beginners
Richard Reed (known to his followers as the HVAC Repair Guy) brings over 17 years of specialized HVAC industry experience. His unique background includes serving as an electrician in nuclear power before completing a 4‑year HVAC service apprenticeship and 8 years of field experience. Based in the Midwest, he has helped homeowners understand, maintain, and upgrade their systems since the early 2000s. His mission is to provide unbiased, “repairman’s point of view” insights into energy conservation and alternative energy solutions.