By Bournemouth Air Conditioning. Published .
Water dripping from the indoor unit is one of the most common faults we see, and the cause is almost always a blocked condensate drain. It is usually a straightforward fix, but it is worth dealing with quickly, because water running down a wall or near electrics does damage over time.
Here is where the water comes from, the usual causes and what you can safely check before you call.
Where the water comes from
When an air conditioning unit cools, warm air passes over a cold coil and moisture in the air condenses on it, the same way a cold glass gets wet on the outside. That water collects in a tray under the coil and runs away through a drain pipe, either outside or into a waste pipe. Where the water cannot fall naturally, the install uses a small condensate pump to lift it.
In heat mode the indoor unit does not normally produce condensate, but the outdoor unit does, particularly when it defrosts. Water dripping from the outdoor unit in winter is normal.
The common causes
- A blocked drain. Dust, slime and sometimes insects build up in the tray and pipe until the water backs up and overflows. This is the most common cause by a distance.
- Dirty filters. Clogged filters restrict airflow, the coil gets too cold and can freeze. When the ice melts there is more water than the tray can handle.
- A failed condensate pump. If your system has one, a stuck float switch or a failed pump leaves the water with nowhere to go.
- Poor fall on the drain pipe. If the pipe was run without enough slope, or has been knocked or kinked, water sits in it instead of draining.
- Low refrigerant. A slow leak can make the indoor coil ice up, and when the ice melts it overwhelms the drain. Under the F-Gas rules a known leak has to be found and fixed, not just topped up.
- A unit that is no longer level. If the indoor unit has shifted on its bracket, water can run to the wrong end of the tray.
What you can check yourself
Switch the unit off at the controller and isolate it before you touch anything. Then:
- Clean the filters, following your user manual.
- Find where the drain pipe comes out outside. Check it is not blocked by leaves, crushed, or frozen at the end on a cold morning.
- If there is a condensate pump, listen for it running and check whether it has a warning light.
- Mop up, and move anything electrical or valuable away from the drip.
Do not push wires up the drain or pour cleaning products into the unit. Leave the coil, the tray and anything inside the casing to an engineer.
Why it is worth fixing quickly
A small drip soon becomes a stained wall, damaged plaster or a damp patch on a ceiling. Water near the indoor unit's electrics is a safety issue. If the cause is ice on the coil, the system is also running inefficiently and may have a refrigerant leak behind it.
If the unit is also struggling to warm the room, the two faults can share a cause. See our guide to using air conditioning to heat your home in winter for what normal winter running looks like.
How servicing prevents it
A service includes clearing the condensate drain and cleaning the coils, which deals with the most common cause before it becomes a problem. Units in kitchens, salons and dusty workplaces may need attention more often than a bedroom unit. Our guide on how often air conditioning should be serviced covers the intervals.
We clear drains and fix leaks on all makes and models, including systems we did not install.
Book a survey or service
If your unit is dripping, see our air conditioning repairs page, or book an air conditioning service. We cover Poole, Bournemouth and across Dorset. Call 07910 686513.
Related services: Air conditioning servicing, Air conditioning repairs.