Why Is My Split System Not Heating: Causes and Fixes

Why is my split system not heating?

In Australia, many homes rely on reverse-cycle air conditioners during cold mornings, winter nights, and sudden temperature drops. But sometimes, problems arise.

The cause could be as simple as the wrong setting, dirty filters, poor airflow, or a blocked outdoor unit. In other cases, it may be low refrigerant, an electrical fault, a sensor issue, or an AC system that is too small for the room.

In this guide, I’ll walk you through the common reasons your split system is not heating, what you can safely check yourself, and when it’s time to call Global Cool Air for a proper inspection.

Quick Checks Before You Call a Technician

Why is my split system not heating?

I always recommend starting with the simple checks first. I have visited numerous homes where the problem wasn’t a major fault. At times, it is in the wrong mode, the timer is operating, or it simply needs a few minutes to warm up.

Before calling Global Cool Air, check these first:

Make Sure It Is on Heat Mode

This sounds obvious, but it is one of the most common things that I see. Your remote control should not be set to COOL, DRY, AUTO, or FAN; it should be set to Heat. It has the AC symbol of a sun. The first thing I would check if my split system suddenly stops heating is the setting.

Set the Temperature Higher Than the Room Temperature

If the air temperature is already 20°C and the remote is at 19°C, the unit might not push hot air to blow into the room. Try setting it to 23°C-24°C and wait.

Don’t panic if your split system is not blowing hot air. A few modern split-system air conditioning units may experience a delay before they start warming up again – particularly on a cold morning in Australia.

Check the Fan Speed and Louvre Direction

Turn the fan on to a medium or high setting. Then point the louvres downwards, to avoid warm air accumulation at ceiling level. If your split system is not heating well, poor airflow direction can make the room feel colder than it actually is.

Check the Remote, Timer, and Sleep Mode

If the screen is dim or not working, change the remote batteries. Ensure that there is no timer, eco mode, or sleep mode affecting performance. I’ve had customers tell me, “My split system is not heating,” only to find the unit was scheduled to shut off after 30 minutes.

Close Doors and Windows

Don’t let the warm air escape. Gaps around windows, doors, and vents can allow warm air to escape, leading to higher heating costs.

Check the Power Supply

Check the circuit breaker and outdoor isolator switch. Your split system heater not working problem may require a technician if the heater’s outdoor unit is not operating even with the indoor unit switched on.

Give It a Few Minutes

In the winter months, a reverse-cycle unit goes through defrost or is in heat standby. Defrosting is a normal phenomenon that occurs during the colder months and can cause a temporary loss of refrigeration until the system clears the frost from the outside unit.

Dirty Filters May Be Blocking Warm Airflow

One of the first things to check is the filter.

Not the fancy parts. Not the wiring. Not the refrigerant straight away.

The filter.

I’ve been to plenty of homes where the owner says, “My split system is not heating,” but the unit is basically trying to breathe through a blanket of dust.

How Dirty Filters Affect Heating

Your air conditioner’s indoor unit depends on clean airflow to move warm air throughout the room. The system could also start up when the filters are clogged, but the airflow becomes weak.

This can make it feel like your split system isn’t blowing hot air, even when the unit is technically on.

Dirty air conditioner filters can significantly affect airflow and energy efficiency, and can impact heating efficiency. 

This is one of the simplest tests to perform if your split system is not heating well, before calling Global Cool Air.

Can You Clean the Filters Yourself?

In most homes, yes. Many split system filters can be removed, vacuumed, washed, dried and put back in the unit. Just be sure to use the manufacturer’s instructions for your model!

Cleaning filters is also included in Energy.gov.au’s basic in-home air conditioner maintenance. 

So, before assuming your split system heater isn’t working, check the filters first.

It is a small job, but it can make a big difference.

If you are not sure how to clean split system AC filters safely, or the split system heating is not working even after cleaning them, Global Cool Air can safely inspect the unit properly. A technician can determine whether the problem is airflow, a clogged coil, a sensor malfunction, or something else.

Filters can also help improve indoor air quality, particularly in homes that have pets, dust, or family members who are allergic.

Check here how often you should clean your AC filters.

The Outdoor Unit May Be Blocked, Frozen, or Not Running

Why is my split system not heating?

Don’t consider only the indoor unit. I know the warm air comes from the unit on your wall, but the outdoor unit is doing most of the work.

Start Outside

I always tell homeowners to check around the outdoor unit first to ensure safety.

When a split system is not heating, blocked outdoor airflow may be the problem. The outdoor unit requires air space. The system can have issues with proper heat transfer if plants, dirt, or clutter surround it.

A Little Frost Can Be Normal

The outdoor unit may frost over on cold Australian mornings. This doesn’t necessarily indicate that your split system heater isn’t working.

Many reverse-cycle systems defrost to loosen frost from the outside heat exchanger coil. Heating may stop for a while during this period, and the indoor or outdoor fan may also turn off. 

But Some Signs Are Not Normal

If the ice persists, the unit continues to shut off regularly, its outdoor fan doesn’t turn on, or strange loud noises are heard, it’s no longer a “wait and see” moment.

At that point, the proper air conditioner repair might be required. A technician can safely inspect the fan motor, sensors, refrigerant, electrical parts, and the outdoor coil.

Low Refrigerant Can Stop the System from Heating Properly

Low refrigerant is one of the issues I do not recommend guessing your way through.

The refrigerant in your air conditioner unit helps transfer heat. It helps pull heat from the outside and transfer it into the house when operating in heating mode. So, if there is a low level of refrigerant, your system can circulate, but not provide adequate warm air.

Refrigerant Should Not Simply Disappear

The key point is that refrigerant is not consumed in the same way as fuel. If your system is low, there may be a leak or an installation issue. 

Leaks are a frequent cause of low refrigerant levels, and a trained technician must repair a leak before the system can be properly recharged.

If, after these basic steps, your split system is not heating well, it’s time to contact Global Cool Air for professional air conditioning services.

We can safely inspect your system, identify leaks, and determine whether the split system heating is not working due to refrigerant or other issues.

Your Split System May Be Too Small for the Room

Sometimes, a split system that isn’t heating isn’t because the unit is broken. It’s simply too tiny for the room.

The size of a split system AC is important because the unit must have sufficient heating power to meet the space’s requirements. The first step to picking the right air conditioner is size, which comes in a variety of heating and cooling capacities. 

If your split system is not heating, it may require a proper load assessment. The air conditioner should be the proper size for the room, not the wall corner where it fits.

The System Could Be Old, Worn, or Losing Efficiency

Age could be a reason your split system is not heating.

If the heating doesn’t seem as robust as before, it doesn’t necessarily mean that it’s not working at all. It may just be old, used, or losing efficiency.

A split system consists of components that have worked hard for years. All components, including fans, sensors, motors, and internal controls, can fail. 

So if your split system is not heating up as it used to, this might be the reason.

Repair or Replace?

If your split system is not heating well and this is the first time it happened, a repair may make sense.

But if your split system heater is still not working, your bills are still climbing, and it is becoming noisy, it may be time to upgrade to a larger size.

At Global Cool Air, when giving advice, we typically consider the age, condition, repair cost, and performance. Sometimes a repair will suffice. Other times, it is more sensible to replace the AC unit rather than pay more for multiple call-outs.

Newer, energy-efficient air conditioners may help reduce running costs. It may be time to shop around for reliable AC brands and compare warranties, parts availability, and efficiency.

Your Thermostat, Sensor, or Control Board May Be Faulty

Sometimes, the unit is not completely dead. It is just confused. 

Your split system relies on sensors to understand the room temperature and decide when to heat, slow down, or stop.

If a sensor is faulty, blocked, or reading the wrong temperature, the unit might shut off too early. 

Problems in your AC sensor may cause it to react incorrectly to room temperature.

We can test the sensors, controller, communication wiring, and board operation safely. This is particularly true if you’re using an inverter-type air conditioner, as its controls are more sophisticated than those of other models, and some problems won’t be apparent on the outside.

Poor Installation Can Affect Heating Performance

The way the unit was installed may be the reason your split system is not heating up properly.

I know that’s not an answer most homeowners would expect. However, as a technician, I have come across systems that were not faulty at all. They were simply added in a way that made heating a bit more difficult than it needed to be.

Placement Matters More Than You Think

Your indoor unit needs to be in a place where the warm air can flow freely through the room. If it’s installed in the wrong corner, at a doorway, or in a space where objects obstruct ventilation, the room might not warm evenly.

The outdoor unit is important too. It requires good air circulation. Outdoor air conditioning units require ventilation for operation, and any barriers should be installed as per the manufacturer’s instructions to prevent damage or poor performance.

When the air conditioner is installed properly, it can heat more efficiently, which helps reduce the risk of performance issues over time.

Sometimes the fix is not just inside the machine. Sometimes it is the way the whole system was set up.

When It Might Be a System Type or Design Issue

A single wall-mounted split system is suitable for heating a single room. But it isn’t magic. It can’t always distribute warm air equally in hallways, doorless bedrooms, and a high-ceilinged open space.

One Unit May Not Heat the Whole Home

I often see this in homes where one indoor unit is trying to heat:

• The living room
• The kitchen
• The hallway
• Two or three bedrooms
• A large open-plan space

That is asking a lot from one system.

Closed Rooms Make Heating Harder

When bedroom doors are closed, air from the living room unit may not circulate throughout the room. This sometimes gives the impression of a split system not heating well, despite the rest of the house being hot.

When Design Needs a Rethink

For some families, multiple ACs may be more convenient, as they allow each room to have its own unit. Some houses would require zoning or a combination of air conditioning units, such as a ducted air conditioner or a multi-split system.

If your split system heater is not working in all rooms, it might not be a fault, but rather a lack of coverage.

When to Call a Professional

You can check the basics yourself: heat mode, temperature setting, filters, airflow, doors, windows, and any blockages on the outdoor unit.

Call Global Cool Air if you notice these signs:

• The unit blows cold air in Heat mode
• The outdoor unit does not run
• Ice keeps forming
• There is a burning smell in your AC
• You notice electrical issues
• Error codes appear
• The system trips the breaker
• Heating is weak after cleaning the filters
• The unit has not been serviced in a long time

Never continually reset the air-conditioner. If your split system is not heating, there could be a more serious problem. Global Cool Air can check the unit correctly and suggest the best solution for your system, not just other types of air conditioners.

Conclusion: A Split System That Won’t Heat Usually Has a Clear Cause

If your split system is not heating, start with the simple checks first. Make sure it is in Heat mode, set the temperature higher, check the filters, inspect the airflow, inspect the outdoor unit, and confirm the power supply is working.

If those checks do not fix it, the issue may be deeper. It could be low refrigerant, a faulty sensor, an electrical problem, poor installation, incorrect sizing, or an older unit that is losing performance.

As a technician, my advice is simple: do not leave it until the cold weather hits hard.

Global Cool Air can help with split system inspections, repairs, servicing, replacements, and new installations. If your system is still not heating properly, book an inspection and get it sorted before peak winter demand.

Contact us before winter comes and experience a comfortable, warmer home when you need it most.