Air conditioning
Why is my air conditioner leaking water?
Water running down the wall under an indoor unit looks like a gas problem and almost never is. In most cases the system is making exactly the water it should, then failing to get rid of it.
6 min read
The short answer
Your air conditioner makes water on purpose
Cold air holds less moisture than warm air. When your indoor unit pulls room air across a cold coil, moisture condenses on the coil the same way it beads on a cold glass in summer. On a humid January afternoon a domestic split system can pull a couple of litres an hour out of a room.
That water runs off the coil into a drain tray, then out through a drain line that falls away to a garden bed, a downpipe or a spoon drain. Most domestic installs have no pump. The whole system is gravity and a clear pipe, so it runs for years without anyone thinking about it. Block the pipe or take away the fall and the tray fills and spills into your room.
What causes the leak
Roughly in the order we find them. The first two account for most of our call-outs in a hot week.
| Cause | What you would notice | Who can deal with it |
|---|---|---|
| Blocked drain line | A steady drip from the bottom of the indoor unit that gets worse the longer it runs. Nothing coming out of the outdoor end of the drain. | A technician. We flush or vacuum the line clear instead of poking at it. |
| Dirty filters icing the coil | Weak airflow for a while beforehand, then water once the ice melts. Sometimes frost on the indoor coil. | You, mostly. Wash the filters and see if it stops. |
| Drain line laid without fall | A leak since installation day or since someone moved something in the roof. | A technician. It is an installation fault that needs re-piping. |
| Cracked or corroded drain tray | A leak that never fully stops, even with clean filters and a clear line. | A technician, who replaces the tray. |
| Indoor unit out of level | Water running off one end of the unit every time. | A technician. Re-hanging the bracket is quick but the unit has to come off the wall. |
| Low refrigerant | Poor cooling as well as water, often with ice on the indoor coil. | A technician. It needs a leak repair, because a sealed system never uses up its refrigerant. |
Only a licensed technician can legally handle refrigerant in Australia. Our tradesmen are Certificate 3 qualified. Standby holds refrigerant trading authorisation AU43504 from the Australian Refrigeration Council.
What to check before you call anyone
Ten minutes of looking will tell you whether you have a filter to wash or a pipe for someone to clear.
- 1
Turn the system off
Cut the power at the isolator or the wall, not just the remote, so it stops making water while you work out what is going on.
- 2
Find where the water gets in
Water travels. A puddle on the floorboards can come from the far end of the unit or from a duct run two metres away. Dry everything and watch where it appears first when the system runs again.
- 3
Pull the filters out
Lift the front panel of a wall unit or drop the return air grille on a ducted system. A filter matted grey with dust restricts airflow enough to freeze the coil, which alone will make a unit leak.
- 4
Find the outside end of the drain line
Look for a small white or black pipe coming out of the wall near the outdoor unit or running into a garden bed. With the system cooling on a humid day it should drip. If it is bone dry while the inside is wet, the line is blocked.
- 5
Run it again and watch
Clean filters and a clear drain sometimes solve it outright. If water comes back within an hour or two, stop running it and call someone.
When to switch it off and leave it off
Ducted systems: the leak you do not see
A wall-mounted split leaks onto your floor, where at least you will notice it. A ducted system keeps its indoor unit in the roof cavity, so the same fault drips into insulation and plasterboard for weeks before a mark shows on the ceiling.
Most ducted installations have a safety tray under the indoor unit with its own drain. It works well until that second drain blocks too, usually because nobody ever looks at it. A brown ring on the ceiling under the unit means the safety tray has already overflowed. Treat that as urgent.
Why drains block faster near the coast
Drain lines silt up with room dust and biological growth, which likes a pipe that is warm, damp and dark. Along the Illawarra two things work against you. Summer humidity keeps the system running long, so there is plenty of water sitting in the line. Salt in the air corrodes outdoor coils and metal drain trays. A pitted tray holds water where a smooth one sheds it.
A service interval that suits a house in western Sydney is a bit generous for a house at Thirroul. The drain line is the part to check more often. It is one of the first things we look at on air conditioning repairs across Wollongong.
What decides the cost of fixing it
A blocked drain and a cracked tray both put water on your floor, but they are very different jobs. The cost depends on which one you have, whether the unit needs taking down, whether the indoor unit sits in a roof cavity or at head height and whether something upstream caused the blockage.
We look at it first, tell you what is wrong and quote a fixed price for the repair before any work starts. Call (02) 4218 3577 if you want to talk it over.
Common questions
- Why is my air conditioner dripping water inside?
- The water it makes is not draining away. It collects in a tray under the coil and leaves through a drain line. When the line blocks, the tray cracks or the unit hangs slightly out of level, the water backs up and spills over the front of the tray. A blocked drain line is the most common cause.
- Is water leaking from an air conditioner dangerous?
- The water is condensation, so it is not toxic. The risk is what it lands on. Water in a wall cavity, across plasterboard or near electrical work causes damage far out of proportion to the fault. If water is dripping near a power point or staining a ceiling, turn the power off and leave the system off until a technician has seen it.
- Why is my air conditioner leaking water outside?
- Usually it is not a fault. The indoor drain line runs outside by design. The outdoor unit also sheds water when it defrosts in heating mode. Get it checked if the outdoor unit drips in cooling mode or the amount of water changes suddenly.
- Does a leaking air conditioner mean it needs regassing?
- Rarely. Be sceptical if that is the first thing you hear. Low refrigerant can cause water indirectly: the coil runs too cold, ice builds on it and the melt overwhelms the tray when the system stops. The tell is ice on the indoor coil alongside poor cooling. A system that cools fine and leaks needs its drainage fixed.