Heat Pump Cools But Does Not Heat (Troubleshooting Guide)

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Quick answer
Confirm the symptom
Tools and prep
Step-by-step troubleshooting
Common causes table
Parts matching
When to call a pro
FAQ
Related guides

Quick answer

If your heat pump cools but doesn't heat, check the thermostat mode, ensure the outdoor unit isn't frozen, and verify the emergency heat setting. If these don't resolve the issue, the problem may involve the reversing valve, auxiliary heat, or electrical faults.

Confirm the symptom

Heat pump cools normally in summer
No heat output in heating mode during winter
Thermostat shows heat demand but no response from the system
Auxiliary heat (emergency heat) does not activate
Outdoor unit fan runs but no heat is produced

Tools and prep

Screwdriver set
Multimeter
Thermal imaging camera (optional)
Safety gloves and goggles
Thermostat manual
Flashlight
Notebook and pen for logging observations

Step-by-step troubleshooting

Check Thermostat Settings
Do: Verify the thermostat is set to 'Heat' mode and the temperature is set above the room temperature.
Observe: Thermostat switches to heating mode and signals the system.
Means: Thermostat was incorrectly set, causing the heat pump to not activate heating.
Next: If the thermostat is correct, proceed to the next step.
Inspect Emergency Heat Setting
Do: Check if the emergency heat (auxiliary heat) is enabled on the thermostat.
Observe: Emergency heat indicator lights up or shows on the display.
Means: Emergency heat was disabled, preventing supplemental heating.
Next: If emergency heat is enabled and still no heat, move to the next step.
Check Outdoor Unit Operation
Do: Look at the outdoor unit to see if the fan is running and if there is any visible ice or frost buildup.
Observe: Outdoor unit fan is running but no heat output, or unit is frozen.
Means: The outdoor unit may be frozen, or the reversing valve is not functioning.
Next: If the unit is frozen, allow it to thaw. If not frozen, proceed to the next step.
Test Thermostat Wiring
Do: Turn off power to the heat pump at the circuit breaker. Remove the thermostat cover and check the wiring connections for looseness or damage.
Observe: Wiring is secure and undamaged.
Means: Loose or damaged wiring prevents the heating signal from reaching the system.
Next: If wiring is secure, continue to the next step.
Verify Reversing Valve Operation
Do: Use a multimeter to test the reversing valve coil for continuity. Check if the valve is receiving power in heating mode.
Observe: Reversing valve coil has continuity and receives power when the system is in heating mode.
Means: The reversing valve is likely faulty or not receiving power.
Next: If the reversing valve is faulty, consider replacing it or contacting a professional.
Check Auxiliary Heat System
Do: Inspect the auxiliary heat (electric resistance heat) components, such as the relays and heating elements.
Observe: Auxiliary heat components are receiving power and functioning correctly.
Means: A fault in the auxiliary heat system prevents supplemental heating.
Next: If auxiliary heat is faulty, repair or replace the affected components.
Inspect Electrical Components
Do: Check the circuit breaker for tripped switches and inspect the electrical connections at the indoor and outdoor units.
Observe: All electrical connections are secure and the circuit breaker is on.
Means: An electrical issue is preventing the heating function from operating.
Next: If electrical issues are found, repair them or consult a professional.
Check for Error Codes
Do: Look for any error codes displayed on the thermostat or control panel of the heat pump.
Observe: Error codes are displayed indicating specific faults.
Means: The system has detected a fault that needs to be addressed.
Next: Refer to the manufacturer's manual to interpret and resolve the error code.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Thermostat Misconfiguration Thermostat set to 'Cool' or emergency heat disabled.	Common	Easy	None
Frozen Outdoor Unit Ice or frost buildup prevents heat absorption from the outside air.	Common	Easy–Medium	Defrosting chemicals (rarely needed)
Faulty Reversing Valve The valve fails to switch between heating and cooling modes.	Sometimes	Medium–Hard	Reversing valve
Auxiliary Heat Failure Electric resistance heating elements or relays are faulty.	Sometimes	Medium	Heating elements, relays
Electrical Issues Loose wiring, tripped breakers, or faulty connections disrupt power.	Sometimes	Medium	Wiring, circuit breaker
Defective Control Board The control board fails to send signals to activate heating components.	Rare	Hard	Control board
Low Refrigerant Level Insufficient refrigerant reduces the system's ability to transfer heat.	Rare	Hard	Refrigerant, professional service
Dirty Air Filter or Ducts Restricted airflow reduces system efficiency and heating capacity.	Sometimes	Easy	Air filter, duct cleaning

Parts matching

If your heat pump's issue is due to faulty components, here are the most likely parts you may need:

Reversing Valve: Required if the system fails to switch to heating mode.
Auxiliary Heat Relays/Heating Elements: Needed if emergency heat does not activate.
Thermostat: Replace if settings are incorrect or unresponsive.
Air Filter: Replace if dirty, reducing airflow and heating efficiency.
Control Board: Replace if electrical signals to heating components are not sent.

Always match part specifications to your heat pump model. Consult a professional for complex replacements like reversing valves or control boards.

When to call a professional

The reversing valve shows no continuity or fails to receive power.
Error codes indicate complex faults like refrigerant leaks or control board failure.
Auxiliary heat components are damaged beyond simple replacement.
Electrical issues involve high-voltage components or main circuit breakers.
You are unsure about handling electrical systems or refrigerant-related repairs.

FAQ

Can a dirty air filter cause my heat pump to not heat?

Yes, a dirty air filter restricts airflow, reducing heating efficiency. Replace or clean the filter regularly.

What is emergency heat, and when should I use it?

Emergency heat is electric resistance heating that supplements or replaces heat pump heating during malfunctions. Use it only when the heat pump is not functioning properly.

How do I know if my reversing valve is faulty?

If the heat pump cools but doesn't heat and the reversing valve coil has no power or continuity, it may be faulty and require replacement.

Why is my outdoor unit frozen?

A frozen outdoor unit is often due to poor airflow, low refrigerant, or a faulty defrost cycle. Allow it to thaw and check for underlying issues.

Can I repair a heat pump's electrical issues myself?

Simple electrical checks like loose wiring can be done safely, but high-voltage repairs should be handled by a licensed technician.