Why Is My Mini-Split Not Working in Heat Mode?

Ductless mini-split heating and air conditioning systems are a great heating and cooling solution for older homes without ductwork, new construction, lake cabins, and home additions alike. Mini-split heating is safer and more efficient than using space heaters, and the cooling is more efficient than window or wall AC units, and even some ducted systems.

For the most part, mini-splits are very dependable. But occasionally, you may find yourself asking “Why is my mini-split not heating?” In this article, we will explore the causes and solutions so you can get your space comfortable again.

There are 5 main causes when a mini-split system is not heating. Some issues you can troubleshoot and fix yourself, while others require professional help.

Check the unit settings on the wall-mounted thermostat/controller (if you have one) or on your mini-split remote. Is the unit actually in heat mode? Do you have the temperature set correctly? This could be an easy fix. Adjust the settings, and consider turning the unit(s) off for several minutes and back on again to clear any glitches in the system.

Poor airflow can also be to blame when your mini-split system isn’t heating. Check the air filters on each indoor unit and clean them as necessary. Clogged filters can restrict airflow. In addition, check the outdoor mini-split heat pump. Clear any debris, snow, or ice from the top of the unit. Shovel away any snow drifts around the unit. Remove or trim shrubs that are closer than two feet away from the ductless heat pump.

Refrigerant issues can also cause a mini-split system to struggle to heat or cool your space. Refrigerant is the lifeblood of the system, and low levels can seriously impact performance and even damage the system. Low refrigerant levels are due to a refrigerant leak, improper charging at the time of installation, or improper mini-split installation.

If you’ve ruled out incorrect settings and restricted airflow, it may be time to call an HVAC professional. If your system is newly installed, call the company that installed it to come fix it. Most companies have a one-year labor warranty so both parts and labor should be covered if the system was installed within the last year.

A frozen evaporator coil in one or more mini-split units can prevent your system from heating or cooling effectively. The coil acts as the heat exchanger in both heating and cooling modes. Frozen coils can be caused by dirty filters, dirty coils, a refrigerant leak, and more. Regular maintenance can help prevent frozen coils. Depending on the cause, you may need to call an HVAC professional.

If your mini-split heat pump compressor or condenser is having issues, it can affect performance. So can failing sensors and internal components on the individual mini-split units inside your home. The older your system gets, the more likely it is that components will malfunction. An HVAC technician will need to troubleshoot the system and make the necessary repairs.

Take care of your mini-split heating and cooling system and it will take care of you. Clean the mini-split filters on each indoor ductless unit regularly to help prevent problems with your ductless HVAC system. Whether you have one mini-split AC and heat unit or a multi-zone mini-split system, make filter maintenance a part of your household routine.

Why? Because dirty or clogged air filters can result in

• Inadequate or no cooling
• Inadequate or no heating
• Water leakage
• Mold and mildew issues
• Musty smell
• System damage

Other DIY maintenance includes keeping the outdoor mini-split heat pump clear of leaves, twigs, and other debris. Trim shrubbery or other plants to keep them at least two feet away from the unit. 

Schedule professional ductless mini-split maintenance twice a year for a ductless mini-split heating and cooling system - once before the cooling season and once before the heating season.

If your system is still under warranty, we recommend scheduling with the mini-split installer you used. For best results, work with an HVAC company that has extensive experience with ductless heating and cooling systems.

During the maintenance visit, the HVAC technician should:

• Thoroughly inspect and clean the outdoor ductless heat pump and indoor mini-split units.
• Ensure the ductless system operates effectively.
• Check for refrigerant leaks.
• Check electrical connections.
• Make minor repairs.

Consider signing up for a maintenance plan and the company will remind you when it’s time to give your mini-split system some TLC.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

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