Why is my aircon leaking water? Causes, fixes, and when to call

If your aircon is dripping water indoors, the most likely cause is a clogged drain line. It's the single most common aircon fault we get called for in Singapore, and the fix is a 30-minute flush that costs around $80-$130.

There are three other causes that look similar but need different fixes. This article walks through how to tell which one you're dealing with, what each one costs, and the small things you can check yourself before calling anyone.

First — should you switch it off?

If water is dripping onto electronics, furniture you care about, or somewhere it could pool and get into electrical outlets, switch the aircon off at the wall first. Place a towel or bucket under the drip and leave it. The unit is designed to handle small water buildup, but ongoing leaking means something is wrong, and leaving it running won't help.

If the water is dripping somewhere harmless, you can leave the unit running until a tech arrives. Just put a tray under it.

The four common causes

1. Clogged condensate drain line (most common)

The condensate drain is a small pipe that carries condensation water away from the indoor unit and out the building. Over months, sludge, mould, and bug debris build up inside it. When the drain backs up, water has nowhere to go, so it overflows out of the tray and drips out of the front of the unit.

How to tell: water is dripping from the front of the indoor unit, usually near the bottom. The unit is still cooling normally. It's often worse when humidity is high.

Cost to fix: $80-$130. We bring a vacuum and a flush kit, clear the line in 30 minutes, and the unit is dry within an hour. If the drain pan also needs cleaning out, that's included.

2. Frozen evaporator coil

Restricted airflow — usually from a heavily clogged filter or a blocked outdoor unit — causes the indoor coil to ice over. When the ice thaws (when the unit cycles off, or you turn it off entirely), all that meltwater overflows the drain pan at once.

How to tell: the cooling has been weak or inconsistent recently. You may see frost or actual ice on the indoor coil when you open the front panel. Water leaks tend to happen in bursts, not as a steady drip.

Cost to fix: $90-$150. The fix involves letting the coil thaw, then cleaning the filter and coil, then checking what caused the airflow restriction. Sometimes this is also a sign the unit is due for a chemical wash.

3. Cracked or shifted drain pan

The drain pan is the plastic tray under the coil that catches condensation before it goes down the drain line. If the tray has cracked from age, or shifted loose during a previous service, water spills out the side instead of flowing into the drain.

How to tell: water is dripping not from the front but from the side or back of the unit. Sometimes you see water marks on the wall below or behind the indoor unit.

Cost to fix: $100-$160. The pan needs to be replaced or re-seated. Includes labour and a new tray if needed.

4. Drain line installed without proper fall

The drain pipe is supposed to slope downward continuously from the indoor unit to the outlet. If a previous install didn't get the fall right — common with DIY jobs or rushed installs — water pools inside the pipe instead of draining out, then eventually backs up into the unit.

How to tell: this is usually a longer-running problem. The leaking has been intermittent for months, and standard drain flushes don't fix it for long.

Cost to fix: $120-$200. We re-route the drain pipe with proper fall, or fit a small condensate pump if the route doesn't allow gravity drainage. Either way, this is the permanent fix and shouldn't need to be done again.

What you can check yourself first

Before calling anyone, two quick checks that occasionally save you a service call:

Clean the filter. Switch the aircon off, open the front panel, slide the filter out, wash it under running water, let it dry, slide it back. If the filter was obviously dusty, run the unit and see if the leak stops after a day. A heavily clogged filter can cause both the frozen-coil leak and weak cooling.

Check the outdoor unit. If the outdoor unit is covered in leaves, dust, or anything blocking airflow, clear it. Same logic: restricted airflow causes ice, which causes leaks.

If the leaking continues after both, you have one of the four causes above, and the next step is a service call.

What you should not do

A few things people try that don't help and sometimes make it worse:

• Don't pour anything into the drain line yourself. Bleach can damage the pan; vinegar can corrode internals. Use only what a service uses (vacuum + proper flush).
• Don't try to top up gas to fix a leaking aircon. Refrigerant level has nothing to do with the water leak. If anyone tells you a gas top-up will fix water leakage, they're wrong.
• Don't ignore it for more than a day or two. A small drip turns into a constant drip turns into water damage to your floor, ceiling, or whatever's below it.

Is it worth doing chemical wash at the same time?

Sometimes, yes. If the leak is caused by a heavily clogged drain or biofilm buildup in the pan, you're already partway into the work that a chemical wash covers. Adding a chemical wash to the same visit is often cheaper than doing it separately a month later.

That said, we won't push it unless the unit genuinely needs it. If the drain flushes cleanly and the coil looks fine, you don't need a chemical wash. We'll tell you on site.

How we quote

WhatsApp us a photo of the indoor unit, where the water is leaking from, and the brand and model. We'll usually be able to tell from the photo whether it's a drain clog or something deeper.

Same-day service is usually available for water leaks. We carry vacuum drain kits, replacement drain pans for common brands, and condensate pumps in the van.

The short version

Aircon water leaks in Singapore are almost always one of four things:

• Clogged drain line — $80-$130 — most common, 30-minute flush
• Frozen coil — $90-$150 — usually a sign filters need attention
• Cracked or shifted drain pan — $100-$160
• Improperly fallen drain pipe — $120-$200 — the permanent fix

If water is dripping somewhere it could damage electronics or furniture, switch the unit off and call. Otherwise, a clean filter and an outdoor-unit check is a fair thing to try first.