Aircon Leaking Water Inside? Here's Why It Happens and How to Fix It
Is your aircon leaking water inside? Learn the most common causes, what you can fix yourself, and when to call a professional technician in Australia.
Is your aircon leaking water inside? Learn the most common causes, what you can fix yourself, and when to call a professional technician in Australia.
You've spotted water dripping from your indoor unit and you're not sure whether to panic or ignore it. If your aircon is leaking water inside the room, that's not normal operation. It's a sign something in the system needs attention. A small amount of condensation on the unit itself is expected, but water actively dripping onto your wall, floor or furniture means one of five common problems is at play. The good news is that most causes of an aircon leaking water inside are straightforward to diagnose, and several can be fixed without calling a technician. This article walks through each cause and what to do about it.
Key takeaways
Water leaking from an indoor unit almost always traces back to one of five issues: a blocked drain line, a dirty filter, a damaged drain pan, low refrigerant or a problem with the original installation. Here's what's actually happening inside the unit for each one.
As your aircon runs, it pulls moisture from the air and that condensate flows out through a drain line to the outside. Over time, dust, mould and algae build up inside the pipe and eventually form a blockage, causing water to back up and overflow into the room. This is the single most common cause of an aircon leaking water inside, and it's also one of the most preventable with regular servicing.
A clogged filter chokes the airflow across the evaporator coil, causing the coil temperature to drop well below freezing. Ice forms on the coil surface, and when the unit cycles off, that ice melts rapidly and dumps far more water into the drip tray than it can handle. This is one of the easiest causes to prevent. Cleaning your filters every four to six weeks during heavy use keeps airflow healthy and the coil temperature where it should be.
The drain pan sits directly beneath the evaporator coil and collects condensate before it flows into the drain line. In older units, the pan can corrode, crack or warp over time, allowing water to bypass the drain entirely and drip straight into the room or ceiling cavity. A cracked pan needs to be replaced rather than patched, as sealants rarely hold long-term in a wet environment.
When refrigerant levels drop, the pressure inside the system falls and the evaporator coil runs far colder than it should, causing ice to form across the coil surface. Once the unit shuts down, that ice melts and the volume of water overwhelms the drain tray. If you suspect a refrigerant leak in your air conditioner, this is a licensed-technician-only repair under Australian regulations. Handling refrigerant without an ARCtick licence is illegal, so don't attempt it yourself.
If the drain line wasn't pitched correctly during installation, water pools in the pipe rather than flowing away under gravity, eventually backing up and leaking inside. Separately, if the foam insulation on the refrigerant pipes deteriorates or was never fitted properly, condensation forms on the exposed pipe surface and drips into the ceiling or wall cavity where you may not notice it until there's real damage. This is exactly why quality installation matters from day one, not just the unit itself.
Before you book a call-out, run through these five steps. Most cases of an aircon leaking water inside are caused by a dirty filter or a partially blocked drain, and both are things you can check and resolve in under 30 minutes. Work through the list in order and only call a technician if the leak continues after step five.
If the steps above do not resolve the leak, the problem is most likely a blocked drain line that needs professional flushing, a cracked drain pan, damaged pipe insulation or a refrigerant issue. These repairs require disassembly of the indoor unit or handling of refrigerants, and must be carried out by a licensed technician. Attempting refrigerant work yourself is illegal in Australia. Book air conditioning repairs with a qualified technician who can diagnose and fix the root cause safely.
Some aircon leaks are a quick DIY fix, but others are a sign of a more serious problem that will get worse if you leave it. If any of the following symptoms apply to your situation, stop the DIY attempts, turn the unit off and book a technician.
If you can see ice forming on the evaporator coil or on the copper pipes running from the indoor unit, the system has a refrigerant or airflow problem that goes beyond a dirty filter. Low refrigerant causes the coil to run far too cold, and no amount of filter cleaning will fix that. A licensed technician needs to check the refrigerant charge and inspect for leaks. Under Australian law, handling refrigerants without an ARC licence is illegal, so this is not a DIY repair under any circumstances.
A cracked or corroded drain pan cannot be reliably patched with sealant in a wet environment. Replacing it requires the indoor unit to be partially disassembled, which means removing the front casing and in some cases the evaporator coil assembly. This is a job for a technician with the right tools and experience, not a weekend project.
If the leak appears to be coming from inside the ceiling or wall rather than directly from the unit, you may have a pipe insulation failure or a drain line that was never pitched correctly during installation. Water sitting inside a wall cavity can cause serious structural damage and mould growth over time. The longer this is left, the more expensive the repair becomes, so treat this as an urgent call-out.
If you have cleaned the filters and the leak has continued for more than 24 hours, the condensate drain line is likely blocked further along than you can reach, or the condensate pump (if your unit has one) may be faulty. Both require professional attention. A standard professional air conditioning service includes a drain line inspection and flush, which clears the kind of deep blockages that cause persistent leaking. It is also a good opportunity to have the technician check the refrigerant charge, coil condition and overall system health while they are on site.
The good news is that none of these repairs are particularly alarming if you catch them early. A technician can usually diagnose and resolve a leaking aircon in a single visit. The main risk is leaving it too long and turning a straightforward drain flush into a ceiling repair.
Preventing an aircon from leaking water inside comes down to two habits: cleaning your filters regularly and booking a professional service once or twice a year. These two steps address the vast majority of leak causes before they become a problem, and they cost far less than a call-out to fix water damage in your ceiling or walls.
Filter cleaning is the single most impactful thing you can do yourself. During heavy use periods, aim to clean your filters every four to six weeks. A clogged filter is the fastest route to a frozen coil and an overflowing drain tray, and cleaning takes less than 15 minutes once you know the routine. Outside of peak season, every six to eight weeks is usually sufficient.
Beyond filters, an annual professional service covers everything else that leads to leaks. For reverse-cycle systems used year-round across both heating and cooling seasons, twice-yearly servicing is worth the investment. A proper service includes drain line flushing to clear mould and algae build-up, evaporator coil inspection, refrigerant level checks and a full assessment of the drain pan and pipe insulation. Frozone Air's air conditioning cleaning service covers all of these checks in a single visit.
A few other habits make a real difference. Keep the area around your outdoor unit clear of debris, garden growth and stored items so airflow is never restricted. Make sure nothing is blocking the return air grille on your indoor unit either, as furniture pushed too close can reduce airflow enough to cause coil icing.
If you are buying a new system, modern units have features that actively reduce the risk of leaks. The Daikin Cora series (e.g. FTXM25Y, 2.5kW, from approx. $1,099) includes a self-cleaning filter function that reduces how often manual cleaning is needed and keeps the drain line cleaner over time. The Mitsubishi Electric MSZ-AP series (e.g. MSZ-AP25VGD, 2.5kW, from approx. $1,049) has a filter indicator light that alerts you when cleaning is due, so you never have to guess. Fujitsu's ASTG series (e.g. ASTG09KMCA, 2.5kW, from approx. $999) includes a drain check function in its self-diagnostic system, which can flag drainage issues early before they show up as a visible leak inside your room.
Finally, make sure any new system is installed correctly from the start. A drain line that is not pitched at the right angle will pool water from day one, no matter how well you maintain the unit. Quality installation is not just about the unit itself.
No, water dripping inside the room from your indoor unit is not normal. A small amount of condensation on the unit casing can occur in very humid conditions, but active dripping onto your wall, floor or furniture means the system has a problem that needs attention. The most common causes are a blocked drain line, a dirty filter or a cracked drain pan.
If your aircon leaks specifically during or after rain, the most likely cause is water entering through the outdoor unit or a poorly sealed wall penetration where the refrigerant pipes pass through. Heavy rain can also overwhelm a partially blocked drain line that was managing fine in dry conditions. Have a technician inspect the wall penetration seals and drain line if this is a recurring pattern.
You should turn the unit off as soon as you notice it leaking water inside. Running the system while it is leaking risks water damage to your ceiling, walls and flooring, and if the cause is a frozen coil, continuing to run the unit makes the problem worse. Turn it off at the wall, clean the filters and wait 30 minutes before restarting to see if the leak resolves.
The cost depends on the cause. A professional drain line flush as part of a standard service typically costs between $150 and $250. Replacing a cracked drain pan or repairing pipe insulation will cost more, generally in the $200 to $400 range depending on the unit and access. A refrigerant recharge is priced separately and varies by system size. Catching the problem early almost always means a lower repair bill.
Most cases of an aircon leaking water inside come down to three things: a blocked drain line, a dirty filter or a refrigerant issue. All three are diagnosable, all three are fixable, and catching any of them early keeps the repair simple and the cost low. Leave it too long and a straightforward drain flush can turn into a ceiling replacement.
If you have worked through the DIY steps and the leak is still going, it is time to hand it over to a professional. Frozone Air services customers across Sydney and Melbourne, and our technicians can diagnose and resolve most leaking aircon problems in a single visit.
Book a service or repair online at frozoneair.com.au, or call us on 1300 801 839. We will get your system running dry again.