Air conditioning
leaking water
Water running down the wall from the indoor unit looks like a burst pipe and almost never is. It is condensate that cannot get out, and in most cases it is a blocked drain rather than a broken machine.
- 89 pounds plus VAT to diagnose, waived if we do the repair
- Any make and any age, including other installers' systems
- We will tell you when a repair is not worth doing
Brands we work with
An indoor air conditioning unit dripping water is almost always a blocked condensate drain or a failed condensate pump. Clearing it costs 120 to 220 pounds. Turn the system off at the remote first: the leak stops when the cooling stops.
It is not refrigerant and it is not dangerous. It is the water the machine pulls out of your air, which has nowhere to go.
What to do in the next five minutes
Turn it off at the remote, not at the wall
Cooling is what produces the water. Stop the cooling and the leak stops within a few minutes. Leave the power on if there is a condensate pump, because the pump may still clear what is in the tray.
Put something under it and look at where the water is coming from
Water from the middle of the unit, running down the wall behind it, is the condensate tray overflowing. Water from one end only is usually the drain connection. Water from the outdoor unit is normal in heating mode and needs nothing done about it.
What actually causes it
| What it is | Why it happens | Typical cost |
|---|---|---|
| Blocked condensate drain | Slime and dust build a plug in the drain line. The tray fills and overflows at the front. | £120 to £220 |
| Failed condensate pump | Where there is no natural fall to a drain, a small pump lifts the water. When it fails the tray fills. | £140 to £260 |
| Drain run with a fall the wrong way | An installation fault rather than a breakdown. It works until the first slime build-up, then never again. | Quoted after inspection |
| Frozen indoor coil, then thawing | Ice forms because of low airflow or low charge, then melts faster than the tray can drain. | £95 to £600 depending on cause |
| Loose or split drain connection | Vibration works the joint loose behind the unit and the water never reaches the pipe. | £120 to £220 |
Prices include labour. VAT is extra. If the fault should still be under manufacturer warranty we will tell you and help you claim rather than charging you for it. Every figure on this site is an estimate based on published UK market ranges and our own installation experience. It is not a quotation. The price you are given after the free survey is the price you pay.
Why a condensate drain blocks in the first place
Cooling air below its dew point takes water out of it, and a hard-working system in a London August can produce a couple of litres a day from one room. That water lands in a shallow tray under the indoor coil and leaves through a small pipe, usually 16mm, which runs outside.
The tray is dark, permanently damp and full of the dust the filter did not catch, which is an excellent place to grow a biofilm. Over two or three seasons that slime narrows the drain until one hot week produces more water than the restriction will pass, and the tray overflows at the lowest point, which is the front edge, which is above your wall.
That is why leaks appear suddenly in a heatwave on a system that was fine in June. The blockage was building for two years; the weather just found it.
What stops it happening again
An annual service, and specifically the part of it people assume is cosmetic. Flushing the condensate line and cleaning the tray is the single maintenance task that prevents this fault, and it is included in the 95 pound service.
If your system has a condensate pump, it has a moving part with a life, and it will eventually fail. A pump that has started to buzz or cycle more often than it did is telling you something, and replacing it before it floods costs the same as replacing it afterwards without the decorating.
What happens when you call us
- You describe the symptom. Half the time that is enough for us to tell you the likely cause and the likely cost before anyone travels.
- We attend and diagnose properly, with instruments rather than by guessing. That is 89 pounds plus VAT.
- You get the cause, the price and an honest answer on whether it is worth repairing, before anything is touched.
- If you go ahead on the same visit, the diagnosis charge comes off.
Other faults
Not cooling
Running but blowing warm air, and the five things that cause it.
Not coolingMaking a noise
What each noise means, and what to do when a neighbour complains.
Making a noiseShowing a code
Verified Daikin and Mitsubishi fault codes, and what each family costs.
Showing a codeRelated
All air conditioning repairs
Every symptom, cause and price in one table, plus when replacing beats repairing.
RepairsAnnual servicing
95 pounds plus VAT. The one thing that prevents most of the faults on this page.
Book a serviceReplacement cost
What a new system costs, for when the repair stops making sense.
See pricesQuestions people ask about this
Is the water dangerous, or is it refrigerant?
It is water. Refrigerant is a gas at the pressures and temperatures in the indoor unit and it would not appear as a puddle. What you have is condensate, the moisture taken out of the room air, and it is no more hazardous than the water on the outside of a cold glass.
It can still do real damage to plaster, paint and anything electrical below it, so it is worth stopping quickly, but there is nothing to evacuate the room for.
Water is dripping from the outdoor unit. Is that a fault?
In heating mode, no. The outdoor coil is the cold one when the system is heating, so it condenses and it also defrosts periodically, and both produce water. A puddle under the outdoor unit on a cold day is the system working correctly.
In cooling mode the outdoor unit should stay dry, so water there in summer is worth a look.
Can I clear the drain myself?
Sometimes, and it is worth a try if you can find the outdoor end of the drain pipe. If you can see it, check it is not blocked by leaves, soil or a wasp nest, which happens more than you would think.
What we would not recommend is pushing anything up the pipe from the outside or putting chemicals down the tray. The tray is thin plastic with an overflow sensor in some models, and a hole in it turns a 140 pound job into a new indoor unit.
How much does it cost to fix?
120 to 220 pounds for a blocked drain, cleared, flushed and tested, and 140 to 260 pounds if the condensate pump has to be replaced. Diagnosis is 89 pounds plus VAT and it is waived if we carry out the repair on the same visit.
Tell us the symptom
Describe what it is doing and we will tell you the likely cause and a realistic price before we come out. Diagnosis is 89 pounds plus VAT and it comes off the repair.
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