Finding water on the floor or wall under your indoor unit is one of those problems that looks worse than it usually is — and also one that gets worse fast if it’s ignored. The good news first: it’s essentially never refrigerant. What you’re looking at is condensation that isn’t draining the way it’s supposed to, and the reason usually falls into one of a handful of predictable causes.
Here’s how we work through it on a service call, so you can figure out roughly what’s going on before booking someone.
| 🗣️ Insight Split systems are effectively small dehumidifiers — cooling the air pulls moisture out of it, and that water is meant to drain away outside through a small hose. A leak indoors almost always means that drainage path is blocked, overwhelmed, or damaged somewhere along the way, not that anything toxic or dangerous is escaping. |
1. Where Is the Water Actually Coming From?
As your split system cools the room, the indoor coil gets cold enough that moisture in the air condenses on it, the same way a cold glass sweats on a humid day. That water is supposed to collect in a small drain pan and flow out through the condensate line to the outside. When it leaks indoors instead, something in that drainage chain has failed.
2. The Most Common Cause: A Blocked Condensate Drain
Over months of use, dust, algae, and general grime build up inside the condensate line and slowly narrow it until water can’t flow through fast enough. Eventually it backs up into the drain pan, overflows, and finds its way out through the front of the unit or down the wall behind it. This is by far the most common reason for an indoor leak, and it’s a straightforward flush for a technician to clear.
3. A Dirty Filter Can Cause This Too
It’s not obvious why a filter would cause a water leak, but the chain of events is simple: a clogged filter restricts airflow across the coil, the coil gets colder than it should, and eventually ice starts forming on it instead of just condensation. When the unit cycles off or you switch it to fan mode, that ice melts all at once — more water than the drain pan and line were built to handle in one go, so it overflows.
If you haven’t checked your filter recently, it’s worth doing before assuming the drain line itself is the problem — see our guide on reusable vs disposable air filters for how to tell which type you have.
| ⚠️ Warning If you notice visible ice or frost on the indoor or outdoor unit, switch the system off and let it fully defrost before running it again. Continuing to run a frozen unit can force water out faster than the drain pan can handle, and in some cases points to a low refrigerant level — which needs a licensed technician to safely diagnose and top up. |
4. Installation Problems: Tilt, Level, and the Outside Hose
Indoor units need a very slight backward tilt so condensation runs toward the drain pan rather than toward the front grille. If a unit was installed slightly off level — or has shifted over time — water can find its way to the wrong side and drip out the front instead of draining properly. It’s also worth checking the drain hose outside: if it’s kinked, crushed, or has come loose from the wall, water that should be exiting outside can back up instead.
| 💡 Pro Tip Before calling anyone, take a look at the outside wall where the drain hose exits. If there’s no water coming out there at all during or after a cooling cycle, that’s a strong sign the blockage is somewhere in the line rather than at the indoor unit itself — useful information to give the technician when you book. |
5. Could It Be a Cracked or Damaged Drain Pan?
On older systems, the plastic drain pan can crack, warp, or develop a hole over years of use, letting water escape before it even reaches the drain line. This isn’t something you can check without opening the unit, so if the drain line is clear and the unit is level but it’s still leaking, a cracked pan is the next thing a technician will look for — particularly on units approaching or past the ten-year mark.
A typical case we see: a customer notices a small drip only during long cooling sessions on humid days, assumes it’s minor, and leaves it for a few weeks. By the time we’re called out, the slow drip has already left a water stain on the ceiling below and started softening the plasterboard. The fix itself — a drain line flush — takes twenty minutes. The water damage repair takes considerably longer and costs a lot more, which is really the main reason not to leave a leak sitting once you’ve noticed it.
6. Is This Urgent, or Can It Wait?
Book a technician promptly rather than waiting if any of these apply:
- The leak is dripping near power points, light fittings, or electrical wiring — switch the unit off at the wall until it’s checked
- There’s already visible staining on the ceiling or wall
- You’ve spotted ice or frost anywhere on the unit
- The leak has been going for more than a day or two
A one-off drip after an unusually humid day, with no staining and no ice, is reasonable to keep an eye on. Anything persistent is worth booking in before it causes water damage rather than after.
7. Why This Shows Up More in Sydney’s Humidity
Higher humidity means your split system is pulling more moisture out of the air to begin with, which puts more load on the drain line and pan than the same unit would see in a drier climate. It’s also why leaks tend to show up more in late spring and summer — exactly when humidity climbs and the system is working hardest.
8. How Do I Stop This Happening Again?
Prevention is mostly the same short list every time: keep the filter clean so the coil doesn’t ice up, have the condensate drain flushed as part of an annual service before the drain has a chance to fully block, and get any small drip checked while it’s still small rather than after it’s caused staining.
Quick-Glance Checklist
- Check the filter first — A dirty filter is a common, easy-to-fix cause
- Look at the outside wall — Is water actually exiting the drain hose?
- Check for ice or frost — If present, switch off and let it defrost fully
- Look for staining on the ceiling or wall near the indoor unit
- Leak near power points? Switch off at the wall and book a technician
- No obvious cause and it’s persisting? Book a drain flush and inspection
Bottom Line
A leaking split system almost always comes down to condensation that isn’t draining properly — a blocked line, a dirty filter, or a levelling issue. None of these are usually expensive to fix, but leaving them running risks real water damage. Catch it early and it’s a quick job.
Still leaking after checking the basics?
Book a split system clean and drain flush and we’ll find exactly where it’s coming from.