Air conditioner leaking water? Causes and what to do

The most common causes of a leak

Nearly every "it's leaking water" call-out we get around Marbella and the Costa del Sol comes down to one of these four causes. The order isn't random — it starts with the most likely.

A blocked drain

By far the most common cause. The pipe that carries condensation away gradually fills with dust, pollen and small debris until the water can no longer reach the outside and overflows the indoor tray instead. On ducted systems the same problem can hit the condensate pump, if the drain can't run by gravity alone.

Dirty filters and ice on the evaporator

A heavily clogged filter cuts airflow over the evaporator, which then overcools and builds up a layer of ice. When you switch the unit off, that ice melts all at once and produces more water than the tray and drain can normally handle — which shows up as a sudden leak right after using the AC.

Low refrigerant

If the leak comes alongside the unit cooling less and less over time, the likely cause is a refrigerant leak: low circuit pressure makes the evaporator freeze up more easily, even with clean filters. You'll find more detail on this fault in our guide to air conditioning not cooling.

An unlevel unit or damaged pipe insulation

If the indoor unit isn't perfectly level, or tilted slightly away from the drain, water can pool on one side of the tray and overflow even with a clear pipe. The same happens if the insulation on the copper pipework is damaged or poorly sealed: condensation forms outside the circuit and drips from a different spot than usual.

What to do if your air conditioner is leaking

While you locate — or wait to have someone check — the cause, it's worth doing things in this order:

• Switch the unit off if the leak is heavy or falling onto furniture, a wooden floor, or near an outlet.
• Protect the area with a cloth or a container while you find the source, to stop water getting into the wall or ceiling.
• Check the filter: if it's very dirty, rinse it with water and let it dry fully before putting it back.
• Check the drain outlet outside: if nothing comes out with the unit running in cooling mode, it's probably blocked.

If the leak carries on after these steps, or you suspect ice on the evaporator or low refrigerant, what comes next needs tools and experience that aren't worth improvising at home: working on the refrigerant circuit without proper training is a real safety risk, and topping up gas without finding the leak first just empties out again before long.

What we do on a leak call-out

When we attend a leak report, we work through the same sequence every time: check the full drain run and clear or unblock it if needed, check for ice on the evaporator, and verify the unit's level and the condition of the pipe insulation. If none of that explains the leak, we measure the circuit pressures to rule out a refrigerant leak. Every visit closes with photos of the problem found and a digital work report. If you'd like to see the full process, we have a dedicated page for air conditioning repair in Marbella.

How to stop it happening again

Most leaks that turn into an urgent call-out could have been caught with regular filter cleaning and a drain check before summer, when the unit starts running for many hours a day. If you'd like to know how often to service your equipment and what a full check-up covers, we have a dedicated guide to AC maintenance on the Costa del Sol.