Why is my air conditioning leaking water?
A blocked drain is the usual cause. Turn the unit off first.
What it usually means
Air conditioning leaking water usually means its drain is blocked. Air con takes moisture from the air as it cools, and that water runs away down a small pipe. If dirt blocks the pipe, the tray under the coil fills up and spills out of the indoor unit.
Turn the unit off when you see it dripping indoors, and keep the water away from anything that could be damaged.
Water outside is a different matter. Aircon dripping water from the outdoor unit, or from the end of the drain pipe, is usually normal. The drain pipe carries water away when the unit cools, and the outdoor unit drips as it defrosts in heating mode.
Sources: Daikin’s operation manual, Mitsubishi Electric’s operating instructions and LG’s support pages.
Other causes of a leak
Four other faults can make an indoor unit leak.
A frozen coil
A frozen coil leaks when the ice melts, because more water reaches the tray than it can clear. Ice forms when a dirty filter starves the coil of air, or when refrigerant runs low. Switch the unit off and give the ice time to thaw. Why a unit stops cooling explains more.
A badly fitted unit
A badly fitted unit can leak from its first day. The indoor unit has to sit level, and the drain pipe has to fall all the way to its outlet. A rise or a dip in the pipe can hold water back, and so can an end sitting in water. Rain can also get in through a badly sealed pipe hole. A leak soon after fitting points here.
A broken condensate pump
A broken condensate pump can’t lift the water away, so the tray fills up and spills. Pumps are used where a drain can’t run downhill, and ceiling cassettes often have one built in. You can’t test a pump from outside the unit, so this one needs an engineer.
A cracked drain tray
A cracked drain tray lets water through before it reaches the pipe. The tray sits inside the casing, so an engineer has to open the unit to find the crack.
Sources: Mitsubishi Electric’s fitting instructions and maintenance sheets, Daikin’s product pages, and LG’s and Samsung’s support pages.
What you can check safely
Five checks are safe to do yourself, and they stop at the filters, the settings and the space around the outdoor unit:
- Turn the unit off with the remote.
- Move anything that could get wet, and catch the drips with a towel or bowl.
- Turn the power off, then wash the filters the way your manual says. Let them dry before you refit them.
- Check the mode and the set temperature, then close the windows and doors. Long running in very humid air can make water drop from a unit.
- Clear leaves, bins or anything else from around the outdoor unit.
Stop there. Don’t open the casing, touch the wiring or push anything up the drain pipe. Don’t rinse the unit or use cleaning sprays on it.
Sources: Daikin’s operation manual and Mitsubishi Electric’s operating instructions.
When it needs an engineer
A leak needs an engineer if it returns after these checks, or if it comes with one of these warning signs:
- water near a socket, a light fitting or other electrics
- water coming through a ceiling, or into a flat below
- ice on the pipes that keeps returning
- an error code, or a light that keeps flashing
- a unit that trips the electrics
If water is near electrics, turn the power off at the fuse box with dry hands, and touch nothing that’s wet.
Book a repair, and say where the water is coming from, because that helps the engineer plan the visit. Clean filters and a clear drain help stop a leak coming back. What a service covers. All our guides cover other problems.
Leak questions
Is a leaking air con dangerous?
A leaking air con can be dangerous if water reaches electrics, so turn it off and keep your hands dry. Left alone, the water can also bring damp and mould, and those can harm your lungs.
Source: GOV.UK on damp and mould.
Can I keep using it while it drips?
No, turn it off until you know the cause. Makers’ manuals say to stop using a unit that leaks indoors. More running means more water, and that can damage whatever sits below it.
Will a service stop it leaking?
A service will stop it leaking if dirt is the cause, because the engineer cleans the filters and the tray and checks the drain. It won’t mend a failed pump or a cracked tray. What a service covers.
Is it leaking refrigerant?
Probably not, if what you can see is water. Refrigerant escapes as a gas with no smell, so it doesn’t leave a puddle. Weak cooling or ice on the pipes are the likelier signs. A refrigerant leak is work for a qualified engineer, by law. What to do about a refrigerant leak.