Mitsubishi Mini-Split Not Heating: Causes and Fixes

Quick Answer

Mitsubishi mini-split not heating: see brand-specific guide above.

When a Mitsubishi mini-split stops heating, nine times out of ten it's one of three things: the outdoor unit is encased in ice because defrost isn't triggering, refrigerant is low from a slow leak, or the reversing valve that switches between heat and cool is stuck. Ignore it and you're risking compressor damage. That's a $1,000+ repair instead of a $30 thermistor.

MitsubishiMinisplitSeverity: moderateDifficulty: intermediate75% DIY Success

Time to Fix

15–90 min

Difficulty

intermediate

Parts Cost

$0 (no parts needed)

Tools Needed

Phillips #2 screwdriver, Flathead screwdriver (for panel clips)

Mitsubishi Mini-Split Not Heating: Causes and Fixes

Mitsubishi mini-splits are genuinely great heaters, but when they quit on you it's usually something specific to how heat pumps work. The outdoor unit pulls heat out of cold air, which sounds wild but works down to about 5°F on Hyper-Heat models and around 20°F on standard units. When something disrupts that process, whether it's ice buildup, a bad sensor, or low refrigerant, you get cold air instead of warm. Most fixes run $50-400 if you catch them early.

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Primary cause35%

Refrigerant20%

Sensor15%

Communication15%

Maintenance15%

Symptoms You May Notice

The indoor unit blows air but it's room temperature or cooler, not warm, and the outdoor unit fan isn't spinning or the compressor sounds like it's short-cycling on and off every few minutes.
Outdoor unit is completely covered in a thick shell of ice, way beyond normal frost, and it's been like that for hours without clearing, meaning defrost just isn't firing.
Unit switches to heating mode on the remote but then automatically kicks back to fan-only after a few minutes, usually with a flashing light on the indoor unit panel.
You can hear the outdoor unit running but heating output drops off dramatically once outside temps fall below 30°F, when it should still be working fine on most Mitsubishi models.
The indoor unit's operation light is blinking in a pattern, which you can decode by counting the blink sequences before and after the pause.

Can you reset a Mitsubishi minisplit to clear the NOT-HEATING code?

Turn the unit off at the remote, then kill the dedicated circuit breaker. Wait a full 3 minutes, not just 60 seconds. Mitsubishi control boards need time to fully discharge before a proper reset. Flip the breaker back on, wait 30 seconds, then turn the unit on from the remote and manually set it to HEAT mode. This usually clears stored soft faults. If the same fault code comes back within 30 minutes of restart, the underlying hardware problem is still there and needs to be addressed.

Tools Required for Diagnosis

Phillips #2 screwdriverFlathead screwdriver (for panel clips)Digital multimeter with ohms settingFlashlight or headlampInfrared thermometerBucket of lukewarm water (for clearing coil ice)

Service / Diagnostic Mode

On the indoor unit, find the EMERGENCY OPERATION button behind the front panel cover (small recessed button, usually on the right side). Hold it for 5+ seconds to trigger a self-diagnostic. The LED will blink a fault code pattern. Count the blinks before the pause as the first digit, after the pause as the second. For wired remote PAR-31MAA: press the CHECK button 5 times within 10 seconds to pull stored fault codes onto the display.

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

ComponentComponent Under Test

Expected Range8000–12000 ohms

ConditionIf Open (OL) or infinite, replace component.

Frequently Asked Questions

Why does my Mitsubishi mini-split stop heating when it gets really cold outside?

Standard Mitsubishi models, the MSZ-GL series, are rated down to about 5°F but start losing significant heating capacity below 20°F. If you're in a climate that regularly sees temps below zero, you really need a Hyper-Heat model like the MSZ-FH or MSZ-JP series, which are rated to -13°F. If your standard model struggles at 25°F, that's actually somewhat expected behavior. But if your Hyper-Heat model is struggling at 25°F, something's wrong, most likely low refrigerant or a defrost system issue that needs to be diagnosed.

Is it normal for my Mitsubishi mini-split to blow cold air for 10 minutes then stop heating?

That's almost certainly a defrost cycle and it's completely normal. Every 30-90 minutes, the outdoor unit goes into defrost mode to melt frost off the coil. During that cycle, the indoor unit either shuts off or blows room-temperature air for about 5-15 minutes. Totally expected. What's NOT normal is if defrost never ends, or if it's running defrost cycles every 10 minutes. That means something's wrong with the defrost control or there's a refrigerant issue causing excessive frost buildup way faster than normal.

How much does it cost to fix a Mitsubishi mini-split that won't heat?

Defrost thermistor is $15-30 for the part, or $80-150 if you hire someone. Refrigerant recharge runs $150-400 depending on how much leaked and what caused it. Reversing valve replacement is $300-600 installed because it's a full refrigerant recover and recharge job. Control board is $200-400 for the part plus labor. If someone quotes you more than $800 for a heating repair on a unit under 10 years old, get a second opinion. Had a customer last month who was quoted $1,200 and it turned out to be a $22 thermistor.

Can I add refrigerant to my Mitsubishi mini-split myself?

No, and not just because it's technically illegal without an EPA 608 certification. Mitsubishi mini-splits are factory charged to very precise specifications and overcharging kills compressors fast. Also, if you're low on refrigerant, there's a leak somewhere. Just topping it off without finding and fixing that leak means you'll be doing this again in 6-12 months. Call a certified HVAC tech for anything refrigerant-related. It's one of the few things on these units that genuinely isn't a DIY job.

My Mitsubishi mini-split has a blinking light but no error code on the remote. How do I read it?

Count the blinks carefully. Mitsubishi uses LED blink codes on the indoor unit when there's no wired remote installed. The pattern is X blinks, a pause, then Y blinks. So 6 blinks, pause, 2 blinks is a 6-2 fault code. Grab your model number and search 'Mitsubishi [your model] LED blink code chart' to decode it. The most common ones I see for no-heat problems are 6-2 (outdoor thermistor fault) and 2-8 (refrigerant system fault). You can also pull the front panel and hold the EMERGENCY OPERATION button for 5 seconds to trigger a diagnostic sequence.

Models Known to Experience NOT-HEATING Errors

This repair applies to most Mitsubishi minisplits with this error code. Common model numbers include:

MSZ-GL06NA, MSZ-GL09NA, MSZ-GL12NA, MSZ-GL15NA, MSZ-GL18NA, MSZ-FH06NA, MSZ-FH09NA, MSZ-FH12NA, MSZ-FH15NA, MSZ-FH18NA

Written by

Raj Patel

HVAC & Water Systems Specialist · 15 years experience

Last verified for technical accuracy on March 17, 2026