Aircon Leaking Water? 7 Common Causes and How to Fix Them

Water dripping from the indoor unit is the single most common aircon complaint we receive. The good news: in most cases it is not a serious fault, and it can usually be fixed in a single visit. The bad news: ignoring it can damage your walls, ceiling, flooring and furniture — and in a condo or HDB flat, sometimes your neighbour’s too.

Here are the seven most common causes, roughly in order of how often we see them.

1. Clogged drainage pipe

Your aircon removes a lot of moisture from Singapore’s humid air. That water flows out through a drainage pipe. Over time, dust, slime and mould build up and block the pipe, so water backs up and overflows from the unit. Fix: a drainage flush, included in every general servicing.

2. Dirty or blocked condensate tray

The tray under the coil collects water before it enters the drainage pipe. When it fills with sludge, water spills over the edges. Fix: a chemical wash or, for heavy build-up, a chemical overhaul.

3. Dirty air filters

Clogged filters reduce airflow over the coil, which can cause it to freeze. When the ice melts, more water is produced than the tray can handle. Fix: wash your filters every 2 to 4 weeks and service regularly.

4. Low refrigerant

A refrigerant leak lowers the pressure in the system, which can also cause the coil to ice up and then drip as it thaws. You may notice frost on the copper pipes or warm air from the vents. Fix: leak detection and gas top-up.

5. Unit not installed level

If the fan coil tilts the wrong way, water collects at the wrong end of the tray instead of flowing to the drain outlet. This is common after renovations or a poor installation. Fix: re-levelling the unit.

6. Damaged or disconnected drainage pipe

Pipes can crack, sag or come loose, especially if they run through false ceilings or cabinets. Fix: replace or re-route the damaged section.

7. Faulty drain pump (cassette and ducted units)

Ceiling cassette units often use a small pump to lift water to the drainage pipe. If the pump fails, water overflows into the ceiling. Fix: drain pump repair or replacement.

What you can safely do yourself

• Switch off the aircon and place a towel or container under the drip.
• Remove and wash the filters with plain water, then let them dry completely.
• Check that the indoor unit looks level.
• Take a photo or short video of the leak to send to your technician.

Avoid poking wires or sticks into the drainage outlet or spraying household chemicals into the unit — you can damage the coil or push the blockage further in.

When to call a technician

If the leak continues after washing the filters, or if you see ice on the pipes, water coming from the ceiling, or water near electrical points, switch the unit off and get it checked. Most leaks are fixed in under an hour.