Heat Pump Not Heating? Here’s How to Troubleshoot

According to Carrier, the most common causes of a heat pump not heating are an incorrect thermostat setting, a tripped circuit breaker, or a dirty air filter. However, if the system is blowing cold air constantly or the outdoor unit is frozen, it may indicate a refrigerant leak or a faulty reversing valve requiring professional repair from  your local Carrier dealer.

2. Inspect Power Sources

• Circuit breaker is tripped: If the heat pump isn't running at all, check your electrical panel. The outdoor unit (usually on a 220v or 240v breaker) and the indoor unit have separate breakers. Reset them if tripped. If they keep tripping, call a professional.
• Outdoor/Indoor power switches: Ensure the dedicated power disconnect switch near your outdoor unit and the power switch on your indoor air handler (which looks like a light switch) are both in the "on" position.

3. Examine Airflow and Filters

• Dirty air filter: A clogged filter restricts airflow, potentially causing the system to shut down or blow lukewarm air. Locate your filter near the indoor unit and clean or replace it. Carrirer recommends checking your filter every 60-90 days and replace or clean it according to the manufacturer's recommendations. For detailed steps, visit our guide on how to change a filter.
• Leaking duct: If airflow is weak and energy bills are rising, you might have leaky ducts. While you can check exposed ducts for leaks by hand, most ductwork is hidden and requires an HVAC contractor to properly diagnose. In a typical home, about 20–30% of the air moving through the duct system can be lost through leaks, holes and poorly connected ducts.^1.

4. Check the Outdoor Unit

• Frozen outdoor unit:  If ice builds up on the outdoor coil or copper tubing, the system cannot transfer heat into your home effectively. While a light frost layer—generally less than 1/4 inch—is normal and should clear during the defrost cycle, ice buildup thicker than 1/4 inch or ice that remains after defrost is not normal and may indicate restricted airflow, low refrigerant or a defrost-system problem. See our article on will a frozen AC fix itself? for more details.
• Blocked outdoor coil: Debris like leaves or cottonwood can clog the outdoor coil, reducing efficiency. Ensure the unit is clear of obstructions. As a general guideline, maintain at least 24 inches of clear space around the outdoor unit, while following the clearance requirements for your specific model.

5. Signs You Need a Professional

• Low refrigerant charge: If the heat pump can't keep up with demand or the coil is frozen, you might be low on AC refrigerant. A Carrier dealer can check the charge and repair leaks.
• Bad reversing valve: If you have a heat pump not heating, but it works perfectly in cooling mode, the reversing valve—which switches the direction of refrigerant flow—may be stuck. This requires a local Carrier expert.
• Frequent defrost problems: Heat pumps periodically enter defrost mode during cold-weather operation to remove frost from the outdoor coil. A typical defrost cycle lasts about 5–10 minutes. If heavy ice remains after the cycle or defrost occurs unusually often, have the system professionally inspected.

Curtis Herchenbach, owner of Herchenbach Mechanical in Gurnee, IL, offers guidance on what homeowners can check themselves versus leave to a professional.