10 Reasons Mitsubishi Mini Split Not Heating (Solved!)

Most Mitsubishi mini split users worry when their unit won’t cool. They barely realize it when it won’t heat until it’s freezing. So, is your Mitsubishi mini split not heating, and you don’t know why?

Your Mitsubishi mini split is not heating because the heat mode is not in effect or the unit is undersized. Other likely reasons include a tripped breaker, clogged filter, blocked outdoor unit, wrong temperature mode, refrigerant leak, frozen coil, or failing compressor or circuit board. 

So, several issues could explain why you have a non-heating mini split, and if you plan to troubleshoot the air conditioning system, you ought to consider all of them. 

To ensure you have an easy time doing it, I’ll explain all the ten causes and their fixes. Moreover, we’ll examine why your Mitsubishi mini split won’t heat in cold weather, why it cools but won’t heat, and why the heat pump is not heating.

Let’s jump into it!

Mitsubishi mini split not heating

In a rush? Below is a quick guide to troubleshooting a non-heating Mitsubishi mini split.

Quick Troubleshooting Guide for A Mitsubishi Mini Split Not Blowing Hot Air

Probable CauseRecommended Fix
1.Heat Mode Not In EffectWait a few minutes for the heat mode to come into effect after powering on the mini split
2.Unit Undersizing Upgrade the size of the unit if it’s too small
3.Tripped BreakerReset the circuit breaker if it’s off
4.Clogged Filter Consider replacing/cleaning the air filter if it’s dirt-clogged
5.Blocked Outdoor UnitClean the outdoor unit to get rid of dirt, debris, and other sources of blockages
6.Wrong Temperature ModeOpt for HEAT mode or AUTO
7.Refrigerant Leak Seek an expert help once you confirm or suspect a refrigerant leakage
8.Frozen Coils Clear ice from the coils and protect your outdoor unit during the cold season
9.Failing Compressor Replace the compressor if it’s faulty, or get a new mini split
10.Failing Control BoardReplace the control board if it’s faulty, or get a new mini split

Why Is My Mitsubishi Mini Split Not Heating?

Generally, here are ten possible explanations for why your Mitsubishi mini split does not heat:

1. The Heat Mode Might Not Have Taken Effect

Usually, it takes a few minutes after turning on the HEAT mode for it to come into effect. So, it doesn’t always indicate something is wrong because your mini split won’t immediately heat. 

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There’s nothing to fix here as it’s not a malfunction. Just wait for a few minutes for the mini split to warm up.

2. The Unit Could Be Undersized (Too Small for The Space)

Unless you match your space with the right air conditioning system, the unit won’t be able to function well. If the AC unit fails to heat, the explanation could be an undersized air conditioner.

That’s why it’s advisable checking the unit’s BTU rating and the space that the manufacturer recommends for it and ensure that’s the case with you. 


If your mini split is too small for your space, consider upgrading it. Get another air conditioning system with a higher BTU rating to match your area.

why is my Mitsubishi mini split not heating

3. The Circuit Breaker Could Be Tripped

Before contemplating expensive repairs, check the circuit box for any tripped circuit breaker. Remember, a tripped breaker disrupts the system’s power supply, making it hard for the HEAT mode to effect.


Reset (turn on) the circuit breaker if it’s off (tripped)

4. The Air Filter Could Be Dirt Clogged

While most of us associate a clogged filter with a non-cooling mini split, it could also explain a non-heating one. The problem with a dirt-clogged air filter is that it compromises the unit’s airflow.  Once there’s limited airflow, the AC is unable to heat. 


Inspect the air filter for dirt clogging. If it’s dirt clogged, replace it if it’s disposable or wash it if it’s reusable. 

5. The Outdoor Unit Could Be Blocked

Your mini split outdoor unit houses essential components such as the compressor, condenser, electrical parts, and fan. Due to regular exposure to weather agents like rain, wind, and snow, you need to maintain it regularly. 

That protects it from accumulating debris, dirt, branches, and other filth, which end up blocking it. Once blocked, the unit can’t breathe and cannot influence functions like cooling and heating.


Check the outdoor unit for dirt, debris, and all manners of filth and clean it. Also, maintain your outdoors to reduce the amount of dirt. 

6. The Temperature Mode Could Be Wrong

If the set temperature on the mini split is lower than the room temperature, the air conditioning system won’t heat. If you select the wrong temperature mode, the mini split won’t heat up.

Ideally, the unit will heat up if the ‘Heat Mode’ is on. And if AUTO Mode is on, the unit may heat or cool depending on the air temperature. However, if you opt for ‘Dry or Cool Mode,’ your mini split won’t heat up but will cool up your space. 

See also  Mitsubishi Air Conditioner Troubleshooting Guide (9 Problems!)


Consider switching the unit to ‘Heat Mode’ if that’s not the case or AUTO mode to allow the AC to automatically heat when the temperature drops. And if you manually adjust the ACs temperature, select a temperature higher than the room temperature.

Mitsubishi mini split cooling but not heating

7. The Refrigerant Could Be Leaking

A low refrigerant level doesn’t just affect mini splits cooling but also heating. Remember, the refrigerant absorbs the room’s hot or cold air. That, however, won’t happen if it’s leaking, perhaps due to poor installation or damage to the unit. 


Overall, it’s not easy to fix a leaking refrigerant DIY. So, I recommend you call an expert. But before you do, it’s good to be sure of the issue.

You can know if the refrigerant is leaking if there are signs of dampness and odd smell around the air conditioning system. 

8. The Coils Could Be Frosty

The condenser and evaporator coils are instrumental in running the mini split. Once they freeze, which is likely to be the case during the winter, your unit cannot breathe correctly.

The ice build-up interferes with the air supply, but that’s not the only thing it does. It can also damage the air conditioner’s plastic parts when they contract and expand. 

Once the AC breaks, the refrigerant will leak, interfering with heating and cooling. 


It’s generally advisable to shield your outdoor unit during the cold season to avoid ice accumulation. And if you notice ice building up, try clearing it. 

9. The Compressor Could Be Failing

The compressor is another essential element of the mini split operations. Once the compressor fails, your mini split cannot cool or heat. 

Unfortunately, diagnosing a non-working compressor is difficult. Hence, leave it to an expert.


You may need to replace the compressor. But before you do, let an expert check the unit to see if the compressor is faulty.

10.  The Circuit Control Board (Power Module) Could Be Failing

If you’ve ruled out all the above nine possibilities, you likely have a failing circuit control board. However, note that once this control board fails, the mini split will not only fail to heat but also to cool. 

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Consider getting a new circuit control board or air conditioning split, depending on preference. 

Mitsubishi mini split heat pump not heating

Mitsubishi Mini Split Not Heating in Cold Weather

In most cases, your mini split fails to heat in cold weather because of ice build-up, which overwhelms the monitor fan and coils. For that reason, it’s advisable to take up these precautions:

  • Cover the outdoor unit – Protect your outdoor unit from ice accumulation by erecting a cover above it. The shield shouldn’t cover its side as that interferes with airflow. So, keep it above the unit. 
  • Raise the outdoor unit — Though you may protect the outdoor unit from falling snow by covering it, that won’t protect it from the ground snow. Thus, you should elevate the unit. 
  • Turn on the defrost setting – You can also turn on your mini split defrost setting to prevent ice build-up and the freezing of the condenser coils.

Mitsubishi Mini Split Cooling but Not Heating

If your Mitsubishi mini split is cooling but not heating, the most likely culprit is one of the following:

  • Ice builds up – Ice, likely to accumulate in the winter, blocks the fan motor and covers the coils making it hard for your mini split to heat.
  • Wrong temperature mode – If you have selected ‘COOL’ mode, you cannot expect your AC to heat. Instead, it’ll cool.
  • Murky coils or filter – If the evaporator or condenser coils are filthy or dusty, the unit may briefly cool but won’t heat. 
  • Tripped breaker – Consider checking your circuit breaker box, as the breaker could be off. So, you’ll need to reset it.

Mitsubishi Mini Split Heat Pump Not Heating

Your Mitsubishi mini split heat pump could fail to heat up because the HEAT mode hasn’t fully kicked in. That takes a few minutes.

It could also be clogged air vents, frosty coils, unmaintained outdoors, or a tripped breaker. So, check out all these issues to see which issue prevents your heat pump from heating.

People Also Ask

1. How Do You Turn On the Heat On a Mitsubishi Mini Split?

You can turn on the heat on a Mitsubishi mini split by first ensuring there is no power interruption in the form of an exploded thermal fuse or tripped breaker. Then, switch the temperature mode to HEAT and wait for the mode to take effect.

2. How Can I Reset a Mitsubishi Mini Split?

To reset a Mitsubishi mini split, spot the reset button at the bottom of the unit and press it. You can also reset it by turning the circuit breaker on and off. 

3. How Should I Troubleshoot My Mitsubishi Mini Split?

You can troubleshoot your Mitsubishi mini split by:

  • Resetting a tripped breaker
  • Cleaning or replacing a clogged filter
  • Defrost frozen coils
  • Fix a leaky refrigerant
  • Replace faulty compressor

Concluding Thought On Mitsubishi Mini Split Not Heating:

Generally, a Mitsubishi mini split that’s not heating is a problem you can troubleshoot. Just ensure you give the heat mode enough time to kick in, reset the breaker if it trips and choose the HEAT mode.

Don’t forget to check issues like a clogged filter, frozen coil, undersized unit, blocked outdoor unit, or failing compressor or control board. 

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