Winter Troubleshooting
Fujitsu Air Conditioner Not Heating
It is a cold morning, you press the heat button and nothing warm arrives. A Fujitsu air conditioner not heating can be a real fault, but it can also be normal behaviour, such as defrost or a slow warm up. This guide helps you tell the difference, run some safe checks and decide when to call for help.
First Things First
Is Your Fujitsu Really Faulty, or Just Doing Its Job?
Reverse cycle heating works differently from a fan heater. Your Fujitsu does not make heat with an element. Instead, it gathers warmth from the outside air and pumps it indoors. That process has a few quirks that can look like faults to a new owner.
For example, the indoor fan may wait a few minutes before blowing. On a frosty morning, the unit may also pause heating to melt ice on the outdoor coil. Both are deliberate. Knowing them saves you an unnecessary call out.
On the other hand, some signs point to a genuine problem. Cold air that never warms, a heating mode that stopped working while cooling still runs, or a lamp pattern that repeats are worth investigating properly.
Probably Normal
A short wait before warm air, brief pauses in very cold weather, or steam rising from the outdoor unit.
Worth Checking
Lukewarm air only, a room that never reaches temperature, or heating that fades after half an hour.
Likely a Fault
Cold air in Heat mode, flashing lamp codes, or a unit that cools happily but refuses to heat.
Normal Behaviour
How Do Hot Start and Defrost Affect Fujitsu Heating?
Two built in routines catch out a lot of Fujitsu owners every winter. Understanding them is the quickest way to avoid worrying over nothing.
Hot Start
When heating begins, the indoor coil starts cold. Rather than blast chilly air at you, the Fujitsu holds the indoor fan back until the coil has warmed. The louvre may open while nothing seems to happen. Give it several minutes before deciding it has failed.
Defrost Cycle
In cold, damp weather, frost builds on the outdoor coil as it pulls heat from the air. Every so often the system reverses briefly to melt it. During defrost, the indoor fan usually stops and the outdoor unit may hiss, click or release a cloud of steam. Heating resumes on its own after a short time.
Room Reached Temperature
Inverter systems slow right down near the set point. The air can feel only mildly warm at that stage, even though the room is comfortable. Raise the set point slightly if you want more output.
If those pauses become very long, or happen every few minutes, that is no longer typical. A faulty outdoor coil sensor or a refrigerant problem can make defrost misbehave, and that needs a technician.
Ranked Causes
Why Is My Fujitsu Blowing Cold Air on Heat Mode?
Once normal behaviour is ruled out, the causes fall into two groups. Start with the left hand list, since most of these take only a few minutes to fix.
Owner Fixable Causes
- The remote is in Cool, Dry, Fan or Auto rather than Heat
- The set point is lower than the current room temperature
- A minimum heat or frost protection setting is active by mistake
- Filters are blocked, so warm air cannot leave the unit
- Leaves, blossom or debris clog the outdoor coil
- A ducted zone controlling the room is switched off
- Weak remote batteries are sending partial commands
Technician Level Causes
- A four way reversing valve stuck in the cooling position
- Low refrigerant charge from a leak somewhere in the circuit
- A faulty outdoor coil sensor upsetting defrost control
- An indoor coil sensor reading incorrectly
- An outdoor fan motor that has slowed or stopped
- Inverter board or compressor faults in the outdoor unit
- Communication problems between indoor and outdoor units
One pattern stands out. If cooling works well in summer but heating has never worked this winter, the reversing valve becomes a strong suspect. That valve redirects refrigerant so the indoor coil becomes the hot side. When it sticks, the unit keeps cooling no matter what the remote says.
Safe Checks
What Should You Try Before Booking a Technician?
The checks below are safe for anyone. None of them involves removing covers or touching electrical parts. Work through them calmly and give the unit time between steps.
Check the Remote Display
Look for the sun symbol or the word Heat. Set the temperature a few degrees above the room. If your remote has a minimum heat button, make sure it is not selected.Swap the Batteries
Cold weather can sap old batteries. Fresh ones remove any doubt that the unit received your setting.Clean the Filters
Turn the unit off and wash the filters in lukewarm water. Dry them fully before refitting. Ducted owners should clean the filter at the return air grille.Inspect the Outdoor Unit
Clear leaves and garden debris from the coil and fan grille. Do not pour boiling water on ice or chip at it, as both can damage the fins.Reset at the Breaker
Switch off at the remote, then at the dedicated circuit breaker. Wait several minutes, restore power and restart in Heat mode.Wait Through the Warm Up
Allow at least ten minutes. Watch for a repeating lamp pattern on the indoor unit and listen for the outdoor fan.
Open more detail
Never open the outdoor unit or try to tap the reversing valve, which some online videos suggest. The valve sits inside a pressurised refrigerant circuit near live electrical parts. In Australia, refrigerant work must be done by an ARCtick licensed technician. Inverter boards can also store a charge after power is removed, so the covers should stay on.
Fault Lamps
Which Fujitsu Error Codes Point to a Heating Fault?
When a Fujitsu stores a fault, the Operation lamp blinks to give the first digit and the Timer lamp blinks to give the second. Our Fujitsu error codes page shows how to read the pattern. Note the code before any reset, because some models clear it on restart.
Code 99
Four way valve fault. The classic code when heating fails but cooling still works.
Code 73
Outdoor coil sensor fault. Defrost timing relies on this reading.
Code 42
Indoor coil sensor fault. Hot start and overheat protection depend on it.
Code 97
Outdoor fan motor fault. No airflow outdoors means no heat to collect.
Code 63
Inverter fault in the outdoor electronics driving the compressor.
Code 11
Lost communication between the indoor and outdoor units.
Other codes, such as 41 for the room sensor or 94 for trip detection, can also stop heating. Whatever the code, it guides the technician toward a circuit. Testing still confirms the actual failed part.
Winter Conditions
How Does Winter Weather in Australian Cities Affect Fujitsu Heating?
Heating output from any reverse cycle system falls as the outside air gets colder. There is simply less warmth available to collect. The effect varies from city to city.
Melbourne and Adelaide Mornings
Cold, damp mornings are prime frosting conditions. Expect more defrost cycles around dawn. A system that struggles only at that time of day may simply be undersized for the room.
Sydney and Perth Winters
Milder winters mean heating complaints often come from units used rarely. A system that sat idle all summer and autumn can reveal a dusty coil or tired fan once heating starts.
Brisbane Cool Snaps
Heating is used only a few weeks a year in Brisbane. Because of that, faults such as a sticky reversing valve may go unnoticed until the first cold night.
Storm Season Damage
A lightning storm or power surge can upset control boards. Some recover after a reset. Others display a fault code and need repair.
Coastal homes face one extra factor. Salt air slowly corrodes outdoor coil fins, which reduces how much heat the unit can draw from outside. Gentle rinsing with a garden hose, on low pressure and with the power off, helps in exposed spots.
Professional Diagnosis
What Does a Technician Test When a Fujitsu Won’t Heat?
Rapid Air Cooling books independent licensed technicians to visit your home. We are not Fujitsu and do not claim manufacturer accreditation. The technicians we send hold the licences their work requires, including ARCtick licensing for refrigerant work.
A heating diagnosis usually starts by confirming that the system is receiving the correct command, then moves outdoors.
- Reads stored codes and checks controller and remote settings
- Measures supply and return air temperatures at the indoor unit
- Checks whether the reversing valve coil is energised in Heat mode
- Watches a full defrost cycle to see if it starts and ends correctly
- Tests indoor and outdoor sensors against expected values
- Checks outdoor fan speed and the condition of the coil
- Uses gauges to assess refrigerant pressures where appropriate
- Explains the cause, repair options and likely next steps
Sometimes the fix is a sensor or a valve coil. Other times it is a leak repair followed by a recharge. Either way, you should get a clear explanation before any work begins.
Keep Using It?
Can You Keep Running a Fujitsu That Won’t Heat Properly?
If the unit is simply slow to warm or pausing for defrost, keep using it. Those are healthy routines. Likewise, if cleaning the filters fixed the problem, carry on.
However, switch off and book a visit if a fault code keeps returning, the outdoor unit is buried in thick ice that never clears, or you smell burning. Running a system low on refrigerant can strain the compressor, which is the most valuable part of the unit. In addition, repeated resets against a protection fault only delay a proper repair.
For general advice that covers every brand, our article on a reverse cycle air conditioner not heating may help. If ice is the main symptom, see the guide to ice on the outdoor unit.
Settings and Features
Could a Fujitsu Setting Be Stopping the Heat?
Fujitsu packs several handy features into its remotes and apps. Occasionally, one of them is the reason a room stays cold. Before assuming a breakdown, look over the settings below.
Minimum Heat Mode
Many Fujitsu models offer a low temperature heating function meant to stop an empty home getting too cold. It holds the room at a very low set point, so it feels like the heater is barely working. Cancel it from the remote to return to normal heating.
Economy Mode
Economy limits the power the system draws. That is useful on a mild day, but on a frosty night it can leave rooms cooler than expected. Switch it off while you test.
Timers and Schedules
An off timer or a weekly schedule may be switching the unit off, or changing the set point, at times you did not expect. Check both the remote and any app schedule.
App and Wi-Fi Control
Supported Fujitsu models can be controlled through Fujitsu’s smartphone app. If another family member has changed settings remotely, the unit may not be doing what the handset shows.
Ducted Fujitsu systems add one more layer. The wall controller, the zone panel and any separate thermostat must all agree. If one room is cold while others are warm, check that its zone is turned on and that the outlet in that room is open.
Ducted Systems
Why Is Only Part of My Fujitsu Ducted System Heating?
Uneven heating across a ducted home is a slightly different problem. The indoor unit may be working perfectly, yet some rooms stay cold. In those cases, the air is simply not reaching them.
Common reasons include a closed zone damper, a crushed or disconnected duct in the roof space, or a blocked return air grille. Warm air also rises, so upstairs rooms often feel warmer than downstairs ones. That is a design consideration rather than a fault.
A technician can measure airflow at each outlet and inspect the ducts. If a damper motor has failed, the zone may be stuck closed, and replacing that motor usually restores heating to the room.
Winter Readiness
How Do You Prepare a Fujitsu for the Heating Season?
The best time to discover a heating fault is in autumn, not on the first freezing night. Run the system in Heat mode for half an hour on a cool day in April or May. If the air comes through warm and steady, you are in good shape.
Also take the chance to wash the filters and clear the outdoor unit. Trim back shrubs that have grown close over summer. If the system is several years old and has never been serviced, consider booking one before winter, when demand is lower and repairs are less stressful.
Finally, think about how you use heating. Setting a moderate temperature and leaving the system running often works better than switching it on and off. Inverter units are most efficient when they hold a steady output.
Find Help
Where Can You Book Fujitsu Heating Repairs?
We arrange heating repairs in five capital cities. Pick your city below, or get in touch and we will help you book.
Our Fujitsu city pages cover local details for Sydney Fujitsu owners, Brisbane, Perth and Adelaide. The national Fujitsu servicing page covers Melbourne. You can also explore every guide on the troubleshooting hub, or start at our air conditioning service Australia homepage.
Questions
Frequently Asked Questions
Why does my Fujitsu take so long to blow warm air?
The hot start routine holds the indoor fan until the coil warms up. This stops cold drafts. A wait of a few minutes is normal, especially on cold mornings.
Why has my Fujitsu stopped in the middle of heating?
It is most likely defrosting the outdoor coil. The indoor fan stops, the outdoor unit may steam, and heating returns shortly after. Frequent or very long pauses are worth checking.
My Fujitsu cools fine but won’t heat. What is wrong?
The four way reversing valve or its control coil is a common cause. A technician can test whether the valve is receiving power and switching properly.
Is steam from the outdoor unit a problem?
No. Steam during defrost is melting frost evaporating off the warm coil. It is a normal part of reverse cycle heating in cold, damp weather.
Can low refrigerant stop a Fujitsu heating?
Yes. Refrigerant carries the heat in both modes. A leak reduces heating and cooling, and a licensed technician must find and repair it before recharging.
Should I use Auto mode for heating?
Auto can switch between heating and cooling based on room temperature. For steady winter warmth, selecting Heat directly usually gives more predictable results.
Can I melt ice on the outdoor unit with hot water?
Please do not. Hot water can damage fins and electrical parts. Let the defrost cycle work. If ice keeps building, book a technician.
Fujitsu Still Blowing Cold?
Book a licensed technician to find out why your Fujitsu is not heating and get the warmth back.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles