Aircon leaking water? 7 causes and how to fix each

Why is my aircon leaking water?

An aircon leaks water indoors when its condensate cannot drain away. The usual cause is a blocked drain pipe or dirty drain pan, followed by a frozen evaporator coil, a unit mounted without enough fall, or torn pipe insulation. Most are fixed in one visit, but a leak that keeps returning means the real cause was missed.

Key takeaways

• Drainage comes first: most indoor leaks start in the drain pan, the drain pipe or the floor trap it empties into.
• Ice means airflow or gas: a frozen evaporator coil from dirty filters or low refrigerant melts and overflows the drain pan.
• Low gas means a leak: the refrigerant circuit is sealed, so low gas always has a leak behind it.
• Drips away from the unit are condensation: water from trunking or a false ceiling usually points to failed pipe insulation.

In the video above, Uncle Eric deals with an aircon that has started leaking water again, which is exactly why finding the root cause matters more than a quick wipe-down.

How do I tell what is causing my aircon leak?

Work through these steps in order. Each one rules a cause in or out.

1. Switch off and protect the area. Turn the aircon off, wipe up the water and move electronics away.
2. Check where the water appears. If it drips from trunking, pipes or a false ceiling away from the unit, it is likely condensation on poorly insulated pipes: see why aircon pipes drip from condensation. If it comes from the unit itself, go to step 3.
3. Check the air filters. If they are grey and matted, airflow is restricted and the evaporator coil may be icing. Rinse and dry them, then run fan-only for an hour before cooling again. If the leak stops, the filters were the cause.
4. Look for ice or frost on the evaporator coil or the small copper pipes. Ice with clean filters points to low refrigerant, which means a gas leak: see signs of an aircon gas leak.
5. Check the drain outlet. Find where the drain pipe empties (floor trap, bathroom, ledge). If the water barely trickles while the unit runs, or the trap is blocked, the drain is clogged.
6. Look at the unit from a distance. If it is tilted, or water runs down one side, the drain pan has lost its fall towards the outlet.
7. Still not sure? The remaining causes are a sludge-blocked drain pan or drain pipe inside the unit, or a failed condensate pump on a ceiling cassette. These need the unit opened. Dripping right now? Message Luna on WhatsApp.

Do not remove the drain pan or poke the drain yourself. Plastic outlets crack easily, and a loose pipe inside the unit is harder to fix than a blockage.

Which leak symptom points to which cause?

What causes an aircon to leak water?

Where does the water come from?

Your indoor unit cools the room by passing warm air over a cold evaporator coil. When that air drops below its dew point, moisture condenses on the coil, like water beading on a cold drink. It runs into the drain pan under the coil, then out through a drain pipe to a floor trap, a common drain or outside.

In Singapore's humidity an aircon produces a lot of water. On humid or rainy days even more condenses, so a drain that is only partly blocked can cope one day and overflow the next.

Blocked drain pipe or floor trap

Dust, slime and biofilm build up inside the drain pipe over months. Eventually water cannot drain fast enough and overflows from the drain pan. Sometimes the pipe is fine and the floor trap it empties into is the blockage. We clear the line with a drain pump or drain opener, then check the outlet and the trap. Watch: chemical drain opener solving a water leak.

Dirty drain pan

The drain pan collects the same slime as the drain pipe. A sludgy pan blocks its own outlet and often smells. When the pan is sludgy or blocked, a chemical wash takes it and the blower fan out and PowerJets them back to as-new, rather than spraying them in place.

Frozen evaporator coil

Clogged filters or a dirty coil restrict airflow, the evaporator gets too cold, and ice forms. When it melts, the drain pan cannot take the sudden volume. A heavily clogged coil needs a deep clean to clear the fins, such as the PowerJet coil clean in premium servicing, or a heavy-duty coil cleaner, an add-on from S$30, when the technician advises it on site.

Low refrigerant

Low refrigerant also freezes the evaporator, with the same melt-and-overflow result. Refrigerant is not used up: if it is low, there is a leak, usually at a flare joint or in a coil, and it has to be found and repaired before recharging.

Not enough fall, or a kinked drain pipe

The drain pan and pipe rely on a slight downward gradient, the fall, towards the outlet. A unit mounted off level, a shifted bracket, or a drain pipe kinked inside trunking all stop the water flowing.

Failed pipe insulation

If the insulation on the refrigerant pipes or drain pipe is torn or squashed, the cold surface sweats and drips, often far from the unit.

Failed condensate pump

Ceiling cassette units usually lift water out with a small condensate pump. If the pump or its float switch fails, water backs up and drips from the panel.

Why does my aircon keep leaking after it was fixed?

A leak that returns usually means the symptom was treated, not the cause. Flushing the drain helps for a while, but if the drain pan and evaporator coil are still full of sludge, the line blocks again. A leak that starts straight after servicing is its own question: see why an aircon leaks after servicing. For how all these parts work together, read how an aircon works and where it goes wrong.

What it costs

When to call a technician

Call us if the leak continues after you have cleaned the filters, if water is coming from a false ceiling or wall, if the unit is also not cooling well, or if it has leaked before. These point to a drain, insulation or gas problem that needs tools to fix. Our aircon repair team handles all of them, with a repair warranty from 180 days (servicing carries 90 days).

You can book online in under a minute, or chat with Luna, our AI assistant, on WhatsApp any time.