Aircon Leaking Water Inside? Causes and Fixes

Your air conditioner is meant to make water. A split system pulls humidity out of the room air, that moisture condenses on the cold indoor coil, and it runs into a drain tray and out through a pipe to the garden. On a sticky February day in Perth a hard-working unit can move several litres.

The water is not the problem. Where the water ends up is the problem. If you are seeing drips down the wall below the head unit, damp carpet, or a brown stain creeping across a ceiling under a ducted system, the drainage path has failed somewhere.

The five usual causes

1. A blocked condensate drain

This is far and away the most common one. The drain line is a narrow pipe, and over a few years it collects dust, insects, and a slimy algae growth that thrives in a dark damp tube. Once it plugs up, the tray overflows and the water takes the next easiest route, which is usually your wall or ceiling.

2. Filthy filters and a frozen coil

Restricted airflow makes the indoor coil drop below freezing. Ice builds up, and when the unit cycles off that ice melts all at once and overwhelms the tray. If you have noticed weak airflow or the unit struggling to cool before the leak started, this is a strong candidate. Cleaning your filters monthly over summer prevents most of it, and there is more detail in our guide on aircon cleaning vs servicing.

3. Low refrigerant

Low gas drops the coil pressure and temperature, which causes the same freeze and thaw cycle as blocked airflow. This one matters because a low system means a leak somewhere, and simply topping it up is not a repair. Read does your aircon need a re-gas before you agree to a gas top-up.

4. Install faults

The drain relies on gravity. If the indoor unit was mounted slightly off level, or the drain line sags, kinks, or was never sloped properly, water pools instead of draining. This shows up as an intermittent leak that appears only on the humid days when the unit produces the most water. It is more common on cheap installs than most people expect.

5. A cracked or corroded drain tray

Older units, and units in coastal suburbs where salt air accelerates corrosion, can end up with a tray that has split or rusted through. This one usually needs a part rather than a clean.

What to do right now

1. Turn the unit off at the wall. Running it will keep pumping water into your ceiling or wall cavity.
2. Put a towel or bucket under the drip and photograph the damage while it is fresh, especially if you are renting or claiming on insurance.
3. Pull out and wash your filters. Warm water, mild detergent, dry completely before refitting. If they were caked, that may well be your answer.
4. Check the outside drain outlet. Find where the drain pipe exits near the outdoor unit. If nothing is dripping out of it while the system runs, the line is blocked.
5. Do not poke wire or high-pressure air into the drain yourself. It is easy to split the pipe inside a wall and turn a cheap clean into a wall repair.

What it usually costs

A drain clear on a wall-mounted split system is a straightforward job and sits at the low end of repair pricing. A ducted system is dearer because the drain and tray usually live in the roof space, and any water damage to the ceiling is a separate trade. Re-levelling a badly installed indoor unit or replacing a corroded tray costs more again.

The expensive scenario is the one where the leak was ignored. Plasterboard, insulation and carpet cost far more than a drain clean, and mould in a ceiling cavity is worse still.

Stopping it happening again

Drains block gradually, so the fix is scheduled attention rather than luck. A yearly service includes flushing the condensate line, which is exactly the maintenance that prevents this failure. Our maintenance plans cover it, or you can start with a one-off health check to find out what condition your system is actually in.

If it is leaking now, get it looked at before the ceiling does. Book a repair or read more about aircon repair, split system servicing and ducted system servicing.