Air conditioning leaking water: causes and what to do
Air conditioning makes water as it cools, and all of it should run away down a drain pipe. When it drips indoors, something is stopping that water getting out. Switch the unit off first, then use this guide to find the likely cause and the checks that are safe to do yourself.
- diagnostic visit, deducted
- £125
- first, if water drips indoors
- Switch off
- are usually normal
- Outdoor drips
- certified engineers
- F-Gas
Why air conditioning makes water
When the unit cools, warm room air passes over a cold coil inside the indoor unit. Moisture in the air condenses on the coil, just like water on a cold glass. It runs into a drain tray under the coil, then out through a small condensate pipe, usually to the outside or into a waste pipe.
Where the pipe can't fall all the way to its outlet, a small condensate pump lifts the water out. On a humid summer day a unit can collect a surprising amount, so even a partly blocked drain soon overflows.
Common causes of an indoor leak
| Cause | Typical signs | Who can fix it |
|---|---|---|
| Blocked drain tray or pipe | Steady drip from the bottom edge of the unit, often after weeks of heavy use | An engineer clears and flushes the drain. Often done within the diagnostic visit |
| Outside end of the drain pipe blocked, crushed or under water | Water backs up and overflows indoors | You can check the outside end. Moving or rerouting the pipe is an engineer's job |
| Dirty filters, so the coil ices up | Weak airflow, ice on the coil or pipes, a flood when it melts | Clean the filters. If ice returns, book a visit |
| Condensate pump failed | Leak on a unit with a pump, sometimes with an error code | An engineer tests and replaces the pump |
| Unit not level or knocked out of line | Water drips from one end of the unit | An engineer re-levels the unit |
| Low refrigerant from a leak | Ice on the pipes, poor cooling | An F-Gas certified engineer finds and fixes the leak |
| Damaged pipe insulation | Drips along the pipe route rather than from the unit | An engineer replaces the insulation |
Water that is normal
Not every drip is a fault. Panasonic's manual lists these as normal: water dripping from the outdoor unit in cooling, from condensation on the cold pipes; water or steam from the outdoor unit in heating, when frost melts during the defrost cycle; and a light mist from the indoor unit in cooling when the air is humid.
If the outdoor unit's defrost water runs across a path, ask us about a better drain point, as it can freeze in winter.
Safe checks you can do yourself
With the unit switched off and isolated, work through these.
- Open the front panel and check the filters. Clean them if they're dusty: vacuum or rinse in lukewarm water, dry in the shade, refit
- Look for ice on the coil behind the filters or on the pipes. If there is, leave the unit off to thaw with a towel underneath
- Find where the drain pipe comes out outside. Check the end isn't blocked by leaves or dirt, squashed, or sitting in a puddle or water butt
- Clear debris from around the outdoor unit and its drain area
- Note when it leaks: only in cooling, all the time, or after a few hours
- Take a photo of the leak, the indoor unit and any error code to send with your booking
What not to do
A blocked drain is usually a quick fix for an engineer, but it's easy to make worse.
- Don't keep running the unit with a bowl underneath. Water can reach the electrics
- Don't push wire, rods or cable ties into the drain from the unit end. The tray and joints damage easily
- Don't pour bleach, drain cleaner or other chemicals into the unit. Daikin warns against solvents and insecticides
- Don't take off covers to reach the drain tray. Inside parts are for a qualified engineer
- Don't touch the sharp aluminium fins of the coil
- Don't loosen or move refrigerant pipes. Only an F-Gas certified engineer may work on them
What a repair visit costs
The diagnostic visit covers the first hour on site. Clearing a blocked drain often fits within it, and if you go ahead with any repair we take the visit off the bill.
- from£125inc. VAT
Repair diagnostic visit
First hour on site, deducted if you go ahead
When to book a repair
Book a visit if water drips indoors after you've cleaned the filters and checked the outside end of the drain, if ice keeps forming, or if the unit shows an error code. Tell us it's leaking when you book, so the engineer brings drain-clearing kit. You get a written price before any work starts.
Our yearly service includes flushing the condensate drain and tray and testing any pump, which catches most blockages before they overflow.
Leaking water questions
Why is my air conditioning leaking water inside?
Most often the drain tray or condensate pipe is blocked, so water overflows from the indoor unit. Other causes are dirty filters making the coil ice up and then melt, a failed condensate pump, a unit that isn't level, or low refrigerant from a leak.
Is it normal for the outdoor unit to drip water?
Yes. In cooling, condensation drips from the cold pipes. In heating, the outdoor unit defrosts now and then and gives off water or steam. Panasonic lists both as normal. Only water from the indoor unit points to a fault.
Can I still use my air con if it's leaking?
No. Switch it off and isolate it. Daikin and Panasonic both say to stop the unit if water leaks from it, because water can reach electrical parts or damage walls and floors.
How do I unblock an air conditioning drain?
You can check the outside end of the pipe is clear and not sitting in water. Clearing the tray and the pipe from the unit end needs the covers off, so it's a job for an engineer, who will flush the drain and check it runs freely.
Why is my air con spitting out mist?
A light mist in cooling on a humid day is normal: cold air from the unit condenses the moisture in the room. Drops of water from the louvre are different and usually mean a drain or icing problem.
Does a leaking air conditioner need regassing?
Usually not. Most leaks are drain problems. If the coil keeps icing up even with clean filters, the refrigerant may be low from a leak, which an F-Gas certified engineer must find and repair before recharging.