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Water Dripping From The Indoor Unit
Water is running down the wall below the indoor head, or dripping off its bottom edge onto the floor.
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What's happening?
An indoor head in cooling mode pulls a surprising amount of moisture out of the air. That water condenses on the cold coil, runs into a tray underneath and leaves through a condensate drain — either falling by gravity to an outside wall or lifted by a small pump into a waste pipe. Water appearing inside the room means the tray has overflowed, and almost always means the drain is the problem rather than the refrigerant circuit. In UK installs the usual culprit is a slime of biofilm growing in the drain line over a summer of constant damp. Less often the pipe was run with a back-fall, the pump has failed, or the tray itself has cracked or shifted. It is worth acting quickly: the indoor head sits above plasterboard, wiring and often a socket.
What usually causes it?
- Condensate drain blocked by biofilm, dust and algae built up in the pipe
- Condensate pump failed, jammed with sludge, or its float switch stuck
- Drain run installed with a level section or a back-fall, so water sits instead of flowing
- Drain tray cracked, displaced, or full of debris that diverts water past the outlet
- Frozen coil thawing and shedding more water than the tray can hold
- Outside end of the drain blocked by a wasp nest, leaves or a garden repair
- Indoor head knocked out of level, so the tray tips away from its outlet
Is it dangerous?
Water and electricity in the same wall is the risk here, not the refrigerant. The indoor head is mains-powered and the wall behind it usually carries cable. Turn the system off at its isolator or the wall switch, put a towel and a bowl underneath, and leave it off until it has been looked at. If water has reached a socket, a light fitting or a consumer unit, turn that circuit off too and treat it as urgent. Ceilings that have been dripped on for days can also give way.
Can I fix it myself?
Turn the unit off first — the leak stops as soon as it stops making condensate. Go outside and find where the drain discharges, usually a small plastic pipe poking through the wall near the outdoor unit, and check whether anything is blocking the end. Clear leaves, spiders and mud from around it. Beyond that, leave it: pouring bleach or drain cleaner into an indoor head damages the tray and the coil, and taking the casing off exposes the fan and the mains terminals.
When should you call an air conditioning engineer?
Call an air conditioning engineer the same week, or sooner if the water is reaching electrics or a ceiling. Also call rather than wait if the leak started immediately after installation or a service, which usually points at pipework fall or a tray fitted wrongly and is the installer's to put right.
What will the air conditioning engineer actually do?
- Isolate the unit, drop the casing and confirm whether the tray is overflowing or the coil is icing
- Clear the condensate line by vacuum or nitrogen purge and flush it through
- Test the condensate pump and its float switch, and replace it if it is not lifting
- Check the fall on the drain run and re-route or re-fix any section holding water
- Clean the coil and tray, which is where the biofilm feeding the blockage grows
- Re-level the indoor head if the tray is tipping the wrong way, and prove the drain under load
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