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Why Is My Mini Split Not Heating? Explained

Your mini-split may not be heating due to one or more of the several reasons. Clogged filters, low refrigerant levels, blocked coils, and miscommunication between the outside and indoor units are usually the main culprits.  

According to a survey conducted by the US Energy Information Administration (EIA), in 2020, 88% of homes in the US used air conditioning in that year. For many of these homes, mini-splits offer a quick and energy-efficient way to provide air conditioning. Unlike conventional air conditioning systems, mini splits are ductless and take up a small space. You can connect up to eight air handlers to a single outside condenser unit.

As with all appliances, your mini split may fail to heat a specific space. If you are in this situation, you have come to the right place. In this article, I will guide you through troubleshooting mini-split heating issues and fixing them. I will share the recommended best practices to increase the life of your mini-split. 

Understanding Your Mini Split

Back in college, my refrigeration class tutor always taught us that the first and vital step in fixing any appliance is understanding how it works. Therefore, I will briefly explain how your mini split works so that it’s easy to identify and fix your mini-split heating problems.

A mini split air conditioning system consists of an outside unit, known as the condenser, and one or more inside units, called air handlers or evaporators. The condenser should be installed on solid footing on the ground or wall of a building with a clear air pathway.  Air handlers can be installed on the ceiling or wall inside your home or building.

Your mini split works like all heating, ventilation, and air conditioning (HVAC) systems. To heat your home, the condenser draws warm air from the outside and pumps it to the air handler inside. The air handler then blows the warm air into your space.

Mini splits are heat transfer systems. Warm air is absorbed from the surrounding air by the refrigerant. A refrigerant has a low boiling point, enabling it to absorb heat even when cold outside. The compressor, housed in the outdoor unit, forces the warm air into the air handler inside the building. The evaporator then evaporates the warm air inside your space.

Now that you have a basic understanding of how your mini split works, it’s time to troubleshoot mini split heating issues.

Troubleshooting Mini Split Heating Issues

Here are the steps you follow when troubleshooting mini split heating issues: 

  1. Check the electrical connection and make sure your mini split is receiving power.
  2. Check your remote to see if the batteries are not flat.
  3. Once you have eliminated steps one and two as the causes of your mini split heating issues, disconnect your unit from the power supply. Now investigate other possible causes of your mini split heating issues, as detailed below.

Clogged Filters

Mini split systems transfer heat by drawing heat from surroundings and blowing hot air. The air has to pass through filters to remove dust and other particles. Over time, the filters get clogged by dust and other particles. If your mini split filters are blocked, they cannot draw sufficient warm air from outside, causing your unit to blow cold air into your room.

How To Fix Clogged Filters

Open both the condenser and air handler units of your mini split and remove the filters. Clean and re-use or replace with new filters, depending on what the manufacturer’s manual recommends. 

A simple and cost-effective way to clean your air filters is to soak them in a vinegar and lukewarm water mixture for 15 to 20 minutes, then use a soft brush to wipe off dust and dirt. You can also use a vacuum cleaner with quick-clean attachments. Leave your filters to dry before replacing them.

Low Refrigerant Levels

Your mini split system uses the refrigerant as a heat transfer agent from the outside to the inside to heat your room or vice versa in the cooling mode. Low refrigerant levels reduce the capacity of your mini split to heat up and transfer enough warm air into your space.

Can you add refrigerant to your mini split yourself? No; under the Environmental Protection Agency EPA regulations, only certified technicians should handle refrigerants. This is because refrigerants are dangerous and can harm the environment if not handled carefully.

Blocked Coils

If your mini split heat pump is not working, dirty coils could be the problem. A common sign that your mini split coils are not working efficiently is the accumulation of ice on the outside of the coils. 

Iced-over coils can not absorb sufficient heat to warm your room. Dirty coils also negatively impact your mini split’s energy efficiency. We have a more comprehensive article on cleaning air conditioner coils.

Low refrigerant levels can also cause mini split coil icing. If you suspect your mini split heating issues emanate from dirty or clogged coils, call a certified technician to fix the problem.

Poor Communication Between The Condenser And Air Handler Units

For your mini split to run efficiently, the condenser and air handler units must communicate and perform their roles. In the heating mode, the condenser absorbs heat from the outside and pumps it to the air handler inside. However, in the cooling function, the process is reversed. The air handler absorbs heat inside your home and expels it outside through the condenser. 

The reverse valve might be faulty if your mini split does not switch from cool to heat mode. This is a fix you can not do yourself. Call a professional to fix it. 

Fixing Cold Air From Mini Split

A faulty mini split can blow cold air into your building despite being in heating mode. Cold air can cause extreme discomfort on a winter day. The table below shows possible causes and fixes for this problem.

Possible CausesHow to Fix
Incorrect thermostat settingsCheck the temperature settings on your mini split. A thermostat responds to the set temperature. Reset temperature settings or contact a professional.
Clogged air filtersClean or replace filters regularly.
Faulty reverse valveA faulty reverse valve can prevent your mini split from changing from the cooling mode to the heating mode.Call a certified technician to fix it.
Refrigerant leaksA faulty reverse valve can prevent your mini split from changing from the cooling mode to the heating mode. Call a certified technician to fix it.

Why Your Mini Split Does Not Reach Set Temperature

Your mini split’s inability to heat the room to the desired temperature might be caused by any of the following:

  • Clogged filters
  • Blocked coils
  • Undersized unit for room size

I have already talked about fixing clogged filters and blocked coils above. Let’s look at your mini split capacity. Your mini split comes with a specified capacity and room size. Add one or more evaporators if your room is too big for a single evaporator. A single condenser can run up to eight evaporators. 

Mini Split Maintenance Tips

You should clean and replace filters to keep your mini split in good condition. Clean or replace filters every one to two months or per your manual’s recommendations. You can watch this YouTube demonstration video on how to clean your mini split deep.  Schedule annual maintenance by a certified mini split heater repair professional.

Trim shrubs or trees around the condenser to maintain a clear air pathway in and out of the unit. In frigid weather, your mini split coils may freeze over, preventing the unit from heating your building. However, your mini split has an auto defrost function that sets in to clear the ice.

To auto-defrost the coils, your mini split reverses the heating mode to the cooling function, blowing cold air into the building. The defrost function allows heat pulled inside the building to heat and defrost the coils.

How can you tell that your mini split is in the defrost mode? The fan in the condenser does not run in the defrost mode. In the cooling mode, the fan runs continuously. Once the coils are completely ice-free, the unit returns to the heating mode and starts warming your space.


Like all appliances, your mini split might have heating problems occasionally. Understanding the root causes of your mini split heating issues will help you identify and fix the problems. Whether it’s a simple fix like filter replacement or professional repair, it’s critical that you urgently take action to restore warmth and comfort in your home.

When fixing your mini split heating issues, observe recommended safety procedures. By following preventative maintenance practices, you can add to the lifespan of your mini split and minimize expensive emergency fixes.


If I suspect a refrigerant leak in my mini split, can I fix it myself? 

No, you cannot fix the leaking refrigerant yourself. Refrigerants can be dangerous to handle. Call a certified professional.

Why is my mini split blowing cold air in the heating mode? 

Your heat pump reverse valve could be faulty. The reverse valve lets your mini split switch from cool to heat mode. Call a professional to fix the valve.

What is the difference between a mini split and traditional central heating systems?

A mini split transmits heat into your room by blowing warm air. It’s ductless. Traditional heating systems transmit heat through ducts fixed to the wall or ceiling.

Can I use my mini split to heat my whole house?

Yes, you can use your mini split to heat your whole house. You can connect up to eight indoor units to a single outside condenser. Each room can have its own air handler.

Why is my mini split emitting a strange odor when heating?

Dust accumulation on heating elements, a malfunctioning fan, or dead rodents can cause foul odors. Inspect your unit and remove any dead pests. The smell of fish indicates an electrical fault. Switch off your mini split immediately and contact a professional.


  • Raoul Hayes

    Raoul Lobo is a seasoned expert in the realm of home appliances and environmental comfort. As a prominent author at, Raoul's passion and expertise shine through in his insightful articles and guides. With years of hands-on experience, he has become a trusted source for readers seeking advice on pools, washers, dryers, and a wide range of other appliances.

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