Why is my air conditioning leaking water?
Water from the indoor unit is almost always condensation, not refrigerant: usually the condensation drain is blocked or the filters are dirty. If the outdoor unit drips while it's heating, it's usually just defrosting and not broken.
LEAKING RIGHT NOW?
First things first
- Switch the air conditioning off with the remote.
- Put a bucket or a towel under the leak, and move anything underneath that could get wet.
- Call us. Tell us the brand and where the water is coming from: under the indoor unit, down the wall or out of the air outlet.
Want to check a few things yourself first? Go through the three checks on the breakdown page.
WHERE THE WATER SHOULD GO
Every air conditioner makes water
When it's cooling or drying, the evaporator in the indoor unit gets cold. Moisture from the room air settles on it, drips into the drip tray (the condensation tray) and runs away through the condensation drain: outside, or through a trap into the sewer.
In the photo, that's the white hose. As long as the water can get away, you won't notice a thing. If it can't, the drip tray overflows and the water comes out under or beside the indoor unit.
It isn't refrigerant. Outside the pipes, refrigerant is a gas: R32, the refrigerant in most split systems on sale today, boils at around minus 52 degrees. If refrigerant leaks, it escapes as a gas, so it leaves no puddle of its own, but the system can start to cool or heat less well.
AT THE INDOOR UNIT
Where the water comes from
This is about a fixed system: an indoor unit in your home and an outdoor unit outside. The first two causes are the ones in the short answer at the top.
| What's wrong | What's going on | What to do |
|---|---|---|
| The condensation drain is blocked | Dust and dirt from the drip tray end up in the drain. Only a little water runs through it, so it doesn't flush itself clean. The water backs up into the unit and drips out. | Switch it off and call us. Clearing the drain is a job for the technician. |
| The filters are dirty | Manufacturers name dirty filters themselves as a cause of dripping water. Less air gets through, and the evaporator can even freeze. | Clean the filters as your manual explains. |
| There's ice on the evaporator | Too little air is getting past it, because of dirty filters, or there's too little refrigerant because of a leak. When the ice melts, it drips out. | Switch it off and call us. If it's a leak, only a certified technician is allowed to work on it. |
| The drain doesn't fall properly, or the unit isn't level | The drain has to run downhill all the way so all the water can get away. If the indoor unit tilts forward, water can even come out of the air outlet. | Call us. The drain needs rerouting or the unit needs levelling. |
| The condensate pump isn't working | If the water can't run away downhill by itself, a small pump moves it. It might sit inside the indoor unit or in the trunking that covers the pipes; on a cassette unit, the technician checks the pump at every service. If the pump fails or gets blocked, the water has nowhere to go. If it's wired up properly, a safety switch stops the air conditioning before the tray overflows. | Switch it off and call us. |
| Drips at the front in muggy weather | If it runs for a long time when the humidity is very high, above 80 per cent, condensation can form on the outside of the unit and on the louvres. That's not a fault. | Keep windows and doors shut while it's cooling, and don't run it for hours on end in weather like this. |
DO IT YOURSELF
What you can do yourself, and what you can't
Do: clean the filters
Switch the air conditioning off with the remote, wait at least five minutes and cut the power. Lift the front cover, take the filters out and vacuum them or rinse them in lukewarm water. Let them dry in the shade and put them back. Manufacturers recommend doing this every two weeks while you're using it.
Don't: the inside or the drain
Don't take the covers off, don't poke at the drain and don't spray anything into the unit. Manufacturers leave cleaning the inside to the technician, and the wrong product can damage the plastic and actually cause leaks.
Beyond the filters, don't put your hands or anything else inside the unit: just look.
AT THE OUTDOOR UNIT
Water at the outdoor unit is usually normal
When you use your air conditioning for heating, the outdoor unit takes heat from the outside air and gets very cold itself. In cold, damp weather, moisture from the air can freeze onto it. Every so often the system defrosts that ice by itself. Water then drips out of the outdoor unit, and sometimes a cloud of steam comes off it. It isn't smoke and it isn't a fault.
Meanwhile the indoor unit stops blowing warm air for a while, and on some brands a light flashes. After anything from a few minutes to a quarter of an hour, it starts heating again by itself.
A little water can come off the outdoor unit when it's cooling too: the pipes and connections get cold, and condensation forms on them.
If the water lands on a balcony or drips onto a patio below, the outdoor unit can be fitted with a drain. Ask about it when you call.
Do call us if ice stays on the outdoor unit, or if it stops getting warm indoors.
PREVENTION
We check the drain at every service
In a Professional Air Conditioning Service, the technician checks the condensation drain. In an intensive clean and a deep clean, they also clean the condensation tray and the drain thoroughly.
With a maintenance plan, your air conditioning gets a service every year, we do the remembering, and you get priority if it breaks down.
Sources
- User's manual, air conditioner SRK15ZS-WF to SRK50ZS-WFMitsubishi Heavy Industries Thermal Systems
- Installation manual for indoor unit, SRK wall unitsMitsubishi Heavy Industries
- Operation manual, room air conditioner CTXM-R and FTXM-RDaikin
- User reference guide FTXF-D and ATXF-DDaikin
- Operating instructions MSZ-AY (multilingual)Mitsubishi Electric
- Mini-Split Leaking Water: Causes and SolutionsTrane
- Mini & maxi orange pump, installation & maintenance manualAspen Pumps
- HL drains for air conditioning and ventilation (in German)Hutterer & Lechner
- Safety Data Sheet Difluoromethane, R32Linde
- Air conditioning and fans (in Dutch)Milieu Centraal
- Regulation (EU) 2024/573 on fluorinated greenhouse gases, Article 10EUR-Lex
- Tips for consumers on servicing and installing air conditioners and heat pumps (in Dutch)Human Environment and Transport Inspectorate
All sources accessed on
WHO ANSWERS
Rein Gerritse
Owner, customer contact and installations
Rein owns Airco Holland together with Peter Reijling. Every article includes what he sees in practice, and he checks it before it goes online.
More about Rein and PeterStill leaking? Give us a call
Switch it off and call. We come out for all the common brands, even if another company installed your system.
READ NEXT
More questions about your air conditioning
Why does my air conditioning smell?
A smelly air conditioner is almost always a dirty one: dirty filters, mould or bacteria on the fins behind the filter, or a dried-out condensation drain. The kind of smell often tells you where to look.
Why has my air conditioning stopped cooling?
First check for yourself that it's set to cool and lower than the room temperature, that the filters aren't full of dust (switch it off first and just look behind the front cover), and that the outdoor unit is clear and free of ice. If it still won't cool after that, give us a call: some refrigerant may have leaked out, and only a certified technician is allowed to work on the refrigerant.