When a Fujitsu air conditioner is not heating, the cause is often a setting or the defrost cycle rather than a fault. A Fujitsu that will not heat is one of the more frustrating faults to diagnose from the couch. This is because several of the things it does when it is working perfectly look exactly like the things it does when something is wrong. It pauses. Cool air may blow for a moment. It stops the outdoor fan and produces a cloud of steam.
Work through the normal behaviour first, then the settings, then the lamps. Many calls about a Fujitsu air conditioner not heating are solved somewhere in the first two groups. The ones that are genuine faults announce themselves clearly once you know what to look for.
Three things that look like faults and are not
The first few minutes of low speed fan
Fujitsu publishes that at the beginning of operation the indoor fan runs at very low speed for 3 to 5 minutes. The older Australian manuals tie it directly to heating and say the unit operates at very low fan speed for about 3 to 5 minutes before switching to the fan setting you chose.
The reason is simple. Blowing hard through a cold heat exchanger just moves cold air around the room. The unit waits until the coil is warm.
Ducted Fujitsu systems do the same thing in a more absolute way. The manual publishes that the indoor fan will not operate until the heat exchanger reaches the set temperature. So on a cold morning a ducted system can be running with nothing at all coming out of the vents for a few minutes.
The defrost pause
This is the behaviour that generates the most calls, and the manual is unusually clear about it. Fujitsu publishes that when outdoor temperature is very low with high humidity, frost may form on the outdoor unit during heating, which reduces performance. An automatic defrost function is fitted.
When it runs, the air conditioner temporarily stops and the defrost circuit operates briefly, for a published maximum of 15 minutes. The ASTG Classic manual narrows that to about 7 to 15 minutes. On a ducted system the manual publishes that the indoor fan shuts down and a defrost icon appears on the controller.
During that period no heat is delivered. That is the design, not a failure. Fujitsu also publishes that during heating the outdoor fan may stop and steam may be seen rising from the unit. That the outdoor unit may emit water. People see steam and reach for the phone, and there is nothing to fix.
The compressor restart delay
Fujitsu publishes that the compressor will not operate for about 3 minutes after certain stops, to protect the circuit. If you have just switched the unit off and straight back on, or the power has blinked, a few minutes of nothing is expected.
Check the mode and the set temperature
The heating range Fujitsu publishes
Across the Australian wall split range, from the current ASTH KNTA and KNCA models back to the ASTG Classic series, Fujitsu publishes a heating range of 16 to 30 degrees. Cooling, dry and auto are published as 18 to 30 degrees. The ducted range publishes 16 to 30 degrees for heat as well.
That matters because 16 degrees is a heating setting many Melbourne homes will never call for. If somebody has nudged the remote down while the unit was in heat, it will sit there doing effectively nothing and still show HEAT on the display.
Check the mode symbol too. Auto and dry both produce airflow that is not heat. A unit in auto will not switch over until its own conditions are met. If you want heat, select heat.
Economy mode is lowering the target for you
Fujitsu publishes economy as a mode that saves electricity by changing the set temperature to a moderate setting. The older manuals put it plainly. Under heating the room temperature will be lower than the set temperature.
So a unit in economy, set to 22, is not trying to reach 22. If the room feels underheated and the ECONOMY lamp is lit on the indoor unit, that is your answer. Turn economy off and see whether the complaint goes away.
The 10 degree heat function on older models
Some older Australian Fujitsu wall splits, including the ASTG Classic series and the ASTG18 to 34 LF range, publish a minimum heat function that maintains the room at 10 degrees to stop it falling too far. It is a frost protection setting for an unoccupied house.
If it has been switched on by accident, the unit will run, the fan will turn, and the room will stay cold. This function is not published on the current ASTH KNTA and KNCA models or on the ducted range. So it only applies if your unit is one of the older series.
When the outdoor temperature is the limit
Fujitsu General Australia publishes an operation range on its product specification pages rather than in the manuals. For the ASTH22KNTA wall split and the ARTG30LHTA ducted unit, heating is published as minus 15 to 24 degrees outdoor dry bulb.
Melbourne never reaches the bottom of that range. So cold is almost never the reason a local system will not heat. It is worth knowing the top of the range though. Heating is published only to 24 degrees outdoors, which is why a system asked to heat on a mild afternoon can behave oddly.
This figure is published per model, so check yours rather than treating those numbers as a blanket Fujitsu specification.
Settings that quietly stop a Fujitsu heating
The weekly timer
This one is worth checking early because the symptom is so odd. Fujitsu General Australia publishes a support note that if all three indoor unit lights flash several times and then turn off. The unit will not start, the weekly timer has been activated. The remote will show WEEKLY. Pressing the weekly button cancels it.
People find this after an hour of troubleshooting a unit that is not faulty at all. If your unit refuses to start and gives you that flash then off pattern, look at the remote display before anything else.
Powerful mode ends on a timer
The current Australian wall split manuals publish powerful operation as maximum power and strong airflow to warm the room quickly, ending 20 minutes after it starts. It also beeps, two short beeps when activated and one when deactivated.
If somebody presses powerful expecting it to stay on and the room cools down again twenty minutes later, nothing has failed. Powerful is not published on the ASTG Classic manual or on the ducted range.
Airflow problems that present as heating problems
A Fujitsu that is heating correctly but cannot move the warm air anywhere will be reported as a heating fault every time. Before assuming the system is at fault, rule these out.
- Blocked air filters. Fujitsu publishes cleaning every 2 weeks in the manuals. The Australian support site suggests at least monthly with daily use
- A ducted return air grille with a filter nobody has touched in a year
- Closed or partly closed vents and zone dampers in rooms that are being complained about
- Airflow direction set to blow along the ceiling, which keeps the warm air above head height
The airflow direction point is worth labouring. Warm air rises, so in heating the louvre wants to be pointing down, not out. A unit that is set for a summer airflow pattern will heat the ceiling very efficiently and leave the room feeling cold.
What the indicator lamps are telling you
The normal lamps
Australian Fujitsu wall splits publish three indicator lamps. OPERATION in green, TIMER in orange and ECONOMY in green. The ASTG Classic adds a fourth, DEFROST in green.
On the Classic, the manual publishes that during automatic defrosting the OPERATION lamp flashes and the DEFROST lamp lights. On the ASTG18 to 34 LF range there is no separate defrost lamp and the green OPERATION lamp simply flashes.
The pattern that means stop
The current manuals publish a specific fault condition. On the indoor unit, OPERATION and TIMER blink while ECONOMY is blinking fast. Fujitsu publishes that you should immediately stop operation, turn off the electrical breaker, and consult authorised service personnel.
The older manuals publish the same instruction in different words. If you notice burning smells, or the OPERATION and TIMER lamps flashing, stop, turn off the breaker and get someone out.
Those are not instructions to work around. A burning smell with a breaker still on is the one situation in this entire guide where the correct response is to stop reading and switch it off.
Why there is no flash count chart here
Plenty of sites publish Fujitsu flash count tables that claim a given number of blinks maps to a given fault. Fujitsu General Australia does not publish such a table in any of its Australian operating manuals. We are not going to reprint someone else version of one and call it manufacturer information.
What Fujitsu does publish is a service check route. The manual publishes that pressing the designated button displays an error code as 2 digit numbers or characters, and instructs you to tell that error code to authorised service personnel. Our Fujitsu error codes guide covers how that display works.
Getting useful information before you call
If you have worked through everything above and the unit still will not heat, five minutes of note taking will shorten the visit considerably.
- The model number, which is on a label on the side or underside of the indoor unit
- Exactly which lamps are lit, which are flashing, and how fast
- Any error code shown on the remote or a wired controller
- Whether the outdoor unit is running, and whether the outdoor fan turns
- Whether the problem is every room or one room, which separates a system fault from a zoning or duct fault
Fujitsu General Australia publishes customer support on 1300 364 484 and its manuals on the product manuals page of its website. One note that confuses people. The Australian Fujitsu General consumer site now trades as GENERAL and Airstage, and the old fujitsugeneral.com.au address redirects there. It is the same company.
Common questions about Fujitsu heating
Why does my Fujitsu blow cold air in heat mode?
Usually because it has just started and is in the published 3 to 5 minute low fan period, or because it is defrosting and has stopped heating for up to 15 minutes. If it blows cold continuously in heat mode with the outdoor unit not running at all, that is a fault worth looking at.
Why does the outdoor unit steam?
Fujitsu publishes that during heating the outdoor fan may stop and steam may rise from the unit because of the automatic defrosting operation. It is normal and it usually lasts a few minutes.
How long should a Fujitsu take to heat a room?
Fujitsu does not publish a heat up time, because it depends on the room, the insulation and the outdoor temperature. What is published is the 3 to 5 minute delay before the fan comes up to speed. If a room that used to warm in twenty minutes now takes two hours, that change is the useful signal.
Should I turn the thermostat up to heat the room faster?
No. Setting 30 when you want 22 does not make the system produce heat faster, it just makes it overshoot and run longer than it needed to. If you want a quick lift on the current range, powerful mode is the published function for it and it ends after 20 minutes.
The unit will not start at all and the lights flashed then went out. What is that?
Check the remote for WEEKLY. Fujitsu General Australia publishes that pattern as the weekly timer being active rather than a fault, and the weekly button cancels it.
Worth doing today
Give it ten minutes before deciding anything is broken. Confirm the mode is heat and not auto or dry, check the set temperature is not sitting near the published minimum of 16, turn economy off, point the louvre downward and let the unit run for a quarter of an hour.
If the lamps show the fault pattern, or there is any burning smell, turn it off at the breaker and stop there. Everything else is worth a filter clean and a second look.
If the unit is heating but never quite gets there, the system may simply be due for a service. Our Fujitsu service and repair page explains what gets checked and when it is worth booking.
For your model’s manual and warranty details, see the official Fujitsu General Australia website.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles