Mini Split Not Heating: The Delay, Mode and Defrost

By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the maker’s manual

Mini Split Not Heating: The Delay, Mode and Defrost

Short answer

Ask for heat and a mini split deliberately blows little or nothing for three to five minutes, so that it cannot blow cold air at you while the coil warms up. A lot of complaints are somebody pressing buttons during that wait. After it, check the mode on the remote, the filters, and whether the outdoor unit is running at all.

A mini split not heating is usually a mini split that has not started yet. Ask one for heat and the indoor fan stays off or barely turns for three to five minutes on purpose, so that it cannot blow cold air into the room while the coil warms up.

A lot of the complaints are somebody standing in front of it during those minutes, pressing buttons, which starts the wait again.

Before you start

What to carry: fresh batteries for the remote, a soft brush and a torch. Twenty minutes.

Gas or electric? Neither. A mini split has no flame and no flue anywhere, so every check here is electrical, airflow, or the refrigerant that a homeowner does not touch.

Check the remote first. A mini split remote sends the whole setting each time, so flat batteries leave the head sitting on whatever it last received. Make sure it says Heat rather than Cool, Dry, Fan or Auto, and that the temperature is well above the room.

Two parts of it that are not do it yourself. The refrigerant. It is not used up, so if it is low there is a leak, usually at a flare joint made when it was installed. A system that heats worse every winter is a system leaking slowly.

The outdoor electrics. Mains comes into the outdoor box and there is a capacitor in there that holds a charge after the power is off. Clearing snow and leaves away is fine. Opening it is not.

The wait before it blows anything

Three to five minutes of little or nothing is the machine being polite, not the machine failing.

Check 1

Set it and walk away for five minutes

Set the remote to Heat, push the temperature well up, and then leave the room.

Behind the scenes the outdoor unit starts and the compressor comes up to speed, and the indoor fan stays off or barely turns until the coil is warm enough to be worth blowing over. Some heads show a small symbol on the display while that happens.

Come back in five minutes. Air that is warm from the first second is the reward for the wait.

If you change the mode or switch it off and on during it, the whole delay starts again, which is exactly why standing there makes it look broken.

Then the ordinary things

Check 2Free to twenty minutes

Mode, temperature, filters

Mode. Heat, not Auto. On a mild day Auto can decide the room needs cooling, and then it does the opposite of what you wanted.

Temperature. Some remotes keep a separate setting for each mode, so the number you set last summer is not the number it is using now.

The filters. Lift the flap on the front of the head and take out the two mesh panels. They are the only filters in the whole system and they clog within weeks: how to get at them and wash them.

The outdoor unit. Go and look. It should be humming with its fan turning. Nothing happening out there is a power or a starting fault rather than a heating one.

It was warm, then it went cold and steam came off outside

That is a defrost cycle and it is normal. In cold damp weather the outdoor coil frosts over, so the unit runs backwards for a few minutes to melt it off. The outdoor fan stops, steam pours off the unit, and the indoor fan usually stops too so it does not blow cold air at you.

Fujitsu says it lasts 7 to 15 minutes, and then it goes back to heating. In the worst weather it can come round as often as once an hour.

What is not normal is a unit that ices up solid and never clears: frost against a real block of ice.

One head heats and another does nothing

On many multi head systems every head has to want the same thing, and the odd one out simply stops.

Check 3Free, five minutes

Walk round and put every remote on Heat

Plenty of multi head systems can only do one thing at a time. Every head has to be in the same mode, and if somebody in another room has set theirs to cooling, the head asking for heat simply sits there doing nothing.

Go round the house and put every remote on Heat, including the ones in rooms nobody uses, then try again.

Systems that genuinely can heat one room while cooling another do exist and they are a more expensive kind. The manual for yours will say which you have.

When it cannot keep up rather than not working

Every mini split loses output as it gets colder outside. An ordinary one falls away below freezing, and a cold climate model holds on much further down.

So a head that heats fine in October and struggles in January may be doing everything it can. Check the rated range for your model before assuming a fault.

What is worth suspecting is a unit that used to cope and now does not. Long runs, weak warm air and odd patches of ice point at low refrigerant, and that means a leak rather than a top up.

Questions people ask

How long should the delay be?

Three to five minutes from cold on most units. Longer than about ten, every time, is worth looking into.

The air feels cool even when it is running.

A heat pump delivers air cooler than your hand, so it feels wrong while it works fine. Measure it rather than trusting a hand: what temperature the air should actually be.

It heats one room fine and another badly.

Check that head’s own filters first, because they clog at different rates. Then check both heads are in the same mode.

The light on the head is flashing.

That is a code, and every maker has its own list. Read it against the manual for your model rather than a list from another brand.

Is it cheaper to leave it on all day?

On an inverter mini split, usually yes. They run most efficiently ticking over at low output rather than being driven hard from cold twice a day.

It smells when it starts heating.

Damp on the coil from the cooling season. Running it in fan mode dries it out, and the filters are the first thing to wash: what each smell means.

Sources: Fujitsu wall mounted operating manual 9315345295-03 (very low fan for about 3 to 5 minutes on a heat start, defrost stops the indoor unit for 7 to 15 minutes, steam off the outdoor unit, multi units in different modes stop), Mitsubishi Electric service manual OBH736 for the MSZ-EF wall units (cold air prevention, defrost stops both fans, Auto can start in Cool, a multi system runs the mode of the first unit), Gree Sapphire service manual (at least 45 minutes of heating between defrosts) and Mitsubishi Electric "Heat Pumps in Extreme Cold Climates" (capacity falls as it gets colder)