Why is my air conditioning leaking water? (and how to stop it)
Water running down the wall from a wall-mounted unit is the single most common call we get. The good news: it's almost never the refrigerant circuit, and it's usually a cheap fix. Here's how to work out which one you've got.
First — is the water from the indoor or outdoor unit?
Water pooling under the outdoor unit is normal. In cooling mode it's condensate; in heating mode it's defrost water. It's not a fault unless it's flooding a path or freezing over.
Water dripping from the indoor unit is not normal and needs sorting before it damages plaster or flooring.
The six common causes of an indoor leak
| Cause | Sign | Fix |
|---|---|---|
| Blocked condensate drain | Drip from the middle or right of the unit, worse on humid days | Drain flush — engineer visit |
| Dirty filters | Weak airflow, then dripping after an hour of running | Wash the filters yourself |
| Frozen coil thawing | Ice visible on the fins, then a sudden gush | Low gas or airflow — engineer |
| Drain line pitched wrong | Leaks from day one of the install | Re-pipe — installer's responsibility |
| Failed condensate pump | Buzzing or silence where you'd hear a click | Pump replacement |
| Cracked drip tray | Constant slow drip regardless of settings | Tray replacement |
What you can safely do yourself
- Turn the unit off at the remote and let it stop dripping before you mop up
- Open the front flap, slide out the two mesh filters, rinse under a warm tap, dry fully, refit
- Check nothing is blocking the outdoor drain outlet — leaves and moss are common
- Run the unit on fan-only for 30 minutes to dry the coil
If it still leaks after clean filters and a dry-out, it's a drain or gas issue and needs an F-Gas engineer.
Why blocked drains happen
The condensate drain is a narrow pipe carrying slightly warm, damp water. Over three to five years a biofilm builds up inside it, the pipe narrows, and water backs up into the tray and over the edge. An annual service flushes it — which is why a leak is usually a sign the system hasn't been serviced, not that it's broken.
What it costs to put right
| Job | Typical cost |
|---|---|
| Drain flush and clean | £90 – £140 |
| Full service including drain | £110 – £160 |
| Condensate pump replacement | £180 – £260 |
| Re-pipe of a badly pitched drain | £200 – £400 |
| Regas after a frozen-coil leak | £180 – £320 |
FAQ
Is it dangerous if my air conditioning is leaking water?
Not to you, but it will damage plaster, skirting and flooring, and a leak caused by a frozen coil means the system is running low on gas and can wreck the compressor. Turn it off and get it looked at.
Can I fix an AC water leak myself?
You can wash the filters and clear the outdoor drain outlet. Anything involving the drip tray, condensate pump or refrigerant needs an F-Gas registered engineer.
Why does my outdoor unit drip water in winter?
That's defrost water — completely normal in heating mode. Only worry if it freezes across a doorway or path.
How quickly can you attend a leak in the West Midlands?
We usually get to leaks within 24–48 hours across Birmingham, Halesowen, Dudley, Solihull and the surrounding towns.
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