Why is My Mini Split Not Heating?

It is winter, and you badly need the supplementary heat from your mini-split pump – which has performed excellently thus far. However, the unit has suddenly stopped blowing hot air, leaving you battling freezing conditions.

Maybe it’s blowing air, but it feels a little colder than usual. Or, maybe it’s not blowing any air at all. What could be wrong, and what can you do about it?

Mini Split Not Blowing Hot Air: Guide to Troubleshooting Common Mini Split Issues

The following are the most common causes of lukewarm heat pump air. It’s not an exhaustive list. The problem could also result from other issues.

1. Everything’s fine. You’re just used to the central furnace

If this is your first time using mini split systems, it’s possible that everything is fine and you’re just not used to these units. Mini splits aren’t as powerful as central furnaces.

Whereas the furnace blows air at 130˚F to 140˚F, heat pumps only release heat at about 85˚F to 92˚F. Therefore, the heat pump’s heat can feel a little lukewarm as you transition from the furnace to a heat pump.

Solution: You need to get used to the new appliance. Why? Because even lowering the thermostat has little effect on supply air (the air is entering your home from the AC). The good news is that it takes only a few days to get used to the new normal.

2. Your body is playing tricks on you

No, this isn’t a joke. As we’ve seen above, heat pumps put out heat slightly below the human body temperature. Whereas the average human body temperature is 98.6˚F, heat pumps release heat from 85˚F to 92˚F.

For this reason, the air from the heat pump may feel colder, even if it’s just a few degrees below body temperature. The issue often worsens when it gets colder outside as the condenser struggles to pull more heat from the colder air.

Solution: You’ll need to get used to the situation. However, if you feel seriously uncomfortable, wrap up and dress warmly. You’ll feel warm again once temperatures outside rise above 40˚F and an auxiliary heating coil kicks on.  

3. The unit is too old

An old mini-split system doesn’t just break down more often; it also has difficulty reaching the desired efficiency levels. For one, wear and tear mean that it’s more likely to lose more heat through gaps in the system. Additionally, the tired motor might not keep up with increased demands, such as when temperatures outside become cold.

Solution: You’ll need even greater maintenance to keep the old ductless air conditioner running effectively. Remember that this can be expensive since you may need to replace several parts. If you reach a point where you’re spending too much on repairs, it might be best to replace the mini-split altogether.

4. The thermostat is broken

The thermostat is the brain of the heat pump. It tells the heat pump what to do and when to do it. Therefore, a broken thermostat can completely mislead the mini-split resulting in confusing heating output.

For instance, if the thermostat is broken, it may keep “tripping” to bogus settings even when you set it at a specific temperature. You may leave it at 90˚F only for it to “trip” to 80˚F the moment you step away.

Solution: You can attempt to fix the thermostat. It’s rarely s straightforward process given the complex nature of thermostats. If the problems keep recurring, consider purchasing a new thermostat. Most units cost well below $20.

5. The thermostat is in auto-recovery

Auto recovery happens when the thermostat is programmed to reach a specified temperature after a specified time. For example, you can schedule your heat pump to reach 70˚F by the time you get home in the evening, say three hours away.

In this case, the thermostat will scale down/up gradually rather than jump to the set temperature right away. If you arrive home before the scheduled time, you may feel a little colder.

Solution: You don’t need to take any action if you still want to reach the specified temperature over the specified duration. However, you can also cancel the programmed setting.

6. Auxiliary heat has failed

Auxiliary heat refers to a supplemental, stand-by heating component installed in your heat pump to provide additional heating when temperatures outside fall below the balance point.

In most cases, it kicks in when temperatures outside the house fall below 40˚F. At this point, most heat pumps can no longer supply enough heat to keep you warm. The auxiliary heating component (if present) will automatically kick in to keep things going. However, it may also refuse to engage no matter how hard the AC tries.

Solution: Most mini-split heat pumps have an indicator that will alert you when aux heat is engaged. If the indicator remains off even in extremely cold weather, you may want to call an HVAC technician.

7. The compressor has failed

The compressor is arguably the most important part of the mini split during heating. It’s tasked with getting air from outside the house into the AC, extracting heat from the air, and sending the heat indoors.

It also ensures continuous circulation of refrigerant to keep the heating process ongoing. As such, a malfunction in the compressor can compromise the entire heating process, making it impossible to send warm air indoors.

Solution: Compressor repair is possible. However, it depends on the specific problem and other factors, such as the age of the unit. For older units, it may be best to replace the unit. Your HVAC technician will advise you accordingly.

8. The air ducts are leaking

On average, 25% of air is lost through leaks. This means that most homes only receive 75% of the total heat generated at the compressor because of air leaks. Standard mini-split systems may not have this problem because they don’t use duct systems.

However, concealed duct mini-split systems are at risk. If the ducts begin to leak, you could lose a lot of heat, resulting in lukewarm heating. The longer the duct pipes, the greater the risk.

Solution: The only solution here is to inspect all accessible ducts and replace the damaged sections. Since you may not be able to access some parts of the ductwork, you may need to call your HVAC technician for assistance.

Other Potential Causes

Although the above eight are the most common reasons why a mini-split heat pump may fail to blow hot air, they aren’t the only reasons.

For example, a failed reversing valve may also result in heating issues. The reversing valve is used to direct the flow of hot or cold air. If the valve is broken, it may get stuck in one direction, thus direct cold air even when the AC is set to heating mode.

Iced evaporator coils are just as bad. If the problem isn’t addressed promptly, the freezing can cause malfunction and prevent the heat exchange process in the compressor.

Key Takeaway

If your mini-split system isn’t delivering warm air during the cold season even after you set it to “Heating Mode,” the issue could be as simple as clogged filters or a bad as a malfunctioned compressor.

Always begin with basic diagnostics, such as cleaning the filter and clearing the ducts. However, if the issue persists, call a professional HVAC technician.