Heat Pump Not Working in Heat Mode (Troubleshooting Guide)

On this page

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

Check the thermostat settings, ensure the air filter is clean, and verify the power supply. If the issue persists, reset the heat pump or consult a professional.

Confirm the symptom

Heat pump runs but does not produce heat
Thermostat shows heat demand but no heating occurs
System works in cooling mode but not heating
No error codes displayed on thermostat or unit
System makes noise but no warm air is produced

Tools and prep

Thermostat manual
Screwdriver set
Vacuum with brush attachment
Multimeter (for voltage checks)
Safety gloves and goggles
Owner's manual for the heat pump
Flashlight for inspection

Step-by-step troubleshooting

Check Thermostat Settings
Do: Verify the thermostat is set to 'Heat' mode and the temperature is set higher than room temperature.
Observe: Thermostat displays correct mode and temperature.
Means: Thermostat is functioning properly.
Next: If settings are correct, proceed to step 2.
Inspect Air Filter
Do: Remove and inspect the air filter for dirt or blockage.
Observe: Filter is dirty or clogged.
Means: Restricted airflow can prevent proper heating.
Next: Replace or clean the filter, then restart the system.
Check Power Supply
Do: Ensure the heat pump's circuit breaker is on and the outdoor unit is receiving power.
Observe: Breaker is tripped or unit is disconnected.
Means: Power interruption may prevent heating mode operation.
Next: Reset the breaker or reconnect power, then test the system.
Reset the Heat Pump
Do: Turn off the power to the heat pump at the circuit breaker for 30 seconds, then restore power.
Observe: System restarts and begins heating.
Means: A temporary reset may resolve minor electrical issues.
Next: If heating resumes, monitor for recurrence. If not, proceed to step 5.
Inspect Emergency Heat Setting
Do: Check if the thermostat has an 'Emergency Heat' option and ensure it is not engaged.
Observe: Emergency Heat is on but not functioning.
Means: Incorrect mode selection can prevent normal heating.
Next: Turn off Emergency Heat and set to regular Heat mode.
Check for Error Codes
Do: Look for any error codes on the thermostat or unit display.
Observe: Error code is displayed.
Means: Specific error codes can indicate the problem area.
Next: Refer to the owner's manual for code interpretation and troubleshooting.
Test Outdoor Unit Operation
Do: Observe the outdoor unit to see if it is running when the system calls for heat.
Observe: Outdoor unit is not running or making unusual noises.
Means: Possible issue with the outdoor unit or its components.
Next: Check for obstructions or ice buildup; if none, consider professional help.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Thermostat Misconfiguration Incorrect settings can prevent the heat pump from entering heating mode.	Common	Easy	Thermostat batteries or replacement
Dirty Air Filter A clogged filter restricts airflow, reducing heating efficiency or preventing operation.	Common	Easy	Air filter
Tripped Circuit Breaker A tripped breaker cuts power to the heat pump, preventing it from operating.	Common	Easy	None
Reversing Valve Failure The reversing valve directs refrigerant flow; failure prevents switching to heating mode.	Sometimes	Hard	Reversing valve
Low Refrigerant Level Low refrigerant reduces heating capacity or prevents the system from functioning properly.	Sometimes	Medium	Refrigerant recharge
Defective Outdoor Fan Motor A non-functioning outdoor fan can prevent proper heat exchange in heating mode.	Sometimes	Medium	Outdoor fan motor
Thermostat Wiring Issues Loose or disconnected wires can disrupt communication between the thermostat and the heat pump.	Sometimes	Medium	Thermostat wiring kit
Frozen Outdoor Unit Ice buildup on the outdoor coil can block airflow and prevent heating.	Rare	Medium	Defrost system components
Defective Control Board A faulty control board can prevent the system from initiating heating mode.	Rare	Hard	Control board
Incorrect Thermostat Type Using an incompatible thermostat can lead to improper system operation.	Rare	Medium	Compatible thermostat

Parts matching

If you need parts for your heat pump, match these common components to your system:

Air filter: Replace every 1–3 months depending on usage
Thermostat batteries: Check annually and replace as needed
Reversing valve: Professional installation required
Outdoor fan motor: Requires electrical knowledge for replacement
Control board: Must match your heat pump model exactly
Defrost timer: Needed if the outdoor unit freezes frequently
Refrigerant: Requires licensed HVAC technician for recharge

Always refer to your heat pump's owner's manual for part specifications and installation instructions.

When to call a professional

The heat pump still does not heat after following all DIY steps
Error codes persist or recur frequently
Unusual noises or smells come from the unit
You suspect refrigerant leaks or electrical issues
The system is over 10 years old and has recurring problems
You are unsure about handling electrical components or refrigerant

FAQ

Why is my heat pump working in cool mode but not heat mode?

This often indicates an issue with the reversing valve or thermostat settings. Check both components for proper function.

Can a dirty filter cause a heat pump to stop heating?

Yes, a clogged filter restricts airflow, which can prevent the heat pump from operating efficiently or at all in heating mode.

How do I know if my heat pump needs refrigerant?

Low refrigerant usually causes reduced heating capacity or no heat. A professional must check and recharge the refrigerant level.

Is it normal for the outdoor unit to not run in heat mode?

No, the outdoor unit should run in both heating and cooling modes. If it doesn't, there may be an electrical or mechanical issue.

What should I do if my thermostat shows 'Heat On' but no heat is produced?

Check the thermostat wiring and ensure the system is receiving power. If everything seems normal, the issue may be with the heat pump's internal components.