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Why is commercial air conditioning leaking water?

Updated 23 October 2026 · SEO Dons Editorial

Why does an air conditioner drip water at all?

Cooling pulls moisture out of the air, and that water has to leave the building. Mitsubishi Electric's guide to customer calls explains that, in cooling mode, water may form and drip from the cool pipes and joints. Daikin starts its drain guidance by telling installers to make sure condensation water can be evacuated properly. A drip is therefore a drainage or insulation question first. Daikin's troubleshooting table gives water leaking from a unit its own entry, with one measure: stop operation. Refrigerant faults show up differently, and the refrigerant leaks guide covers them.

What causes commercial air conditioning to leak water?

Installation manuals from two major makers point to the same short list.

CauseWhat the manufacturer's manual says
Wrong fall, or an air vent in the drainMitsubishi Electric's manual for its PEFY ducted units calls for drain pipework falling by more than 1/100 towards the discharge side, with no trap or irregularity on the way, and says never to fit an air vent pipe because the drain may be ejected.
Unit not levelThe same manual says to install the unit horizontally: if the side with the drain port is higher, water leakage may be caused.
Pump or drain-system faultDaikin's VRV IV code list includes drain system and drain malfunctions on the indoor unit. Mitsubishi's manual says to confirm the drain-up mechanism operates normally and that connections do not leak.
Poor hose connectionDaikin says incorrect connection of the drain hose might cause leaks and damage the installation space and surroundings.
Uninsulated drain pipes or ductsDaikin says to insulate the complete drain piping. Mitsubishi calls for anti-sweating insulation on drain pipes, and full insulation on duct flanges to prevent condensation.
Humidity beyond the unit's rangeDaikin's operating-range note says the humidity limit exists to avoid condensation and water dripping out of the unit, and beyond it safety devices may stop the system.
Airflow settingDaikin warns that one airflow direction setting may cause dew or dust to settle on the ceiling or flap.

A coil that has iced up is a different case. Ice formation and insufficient cooling capacity are on the leakage regulation's list of grounds to suspect a refrigerant leak, so a unit that drips and also ices or fails to cool needs an F-gas engineer rather than a drain clear. The guide to air conditioning not cooling covers the airflow and control causes of weak cooling.

What can a site team check safely?

  1. Stop the unit. Daikin's table says to stop operation when water leaks from the unit, and warns that a wet indoor unit risks electric shock or fire. Isolation and anything near live parts belong to a competent person: Regulation 16 of the Electricity at Work Regulations 1989 bars anyone from work needing technical knowledge unless they have it or are suitably supervised.
  2. Contain the water. HSE lists drip trays among the ways to control contamination, and notes that on a smooth floor only a tiny amount of liquid is enough to cause a slip risk.
  3. Record it. Note the unit, the room, the time and any fault code. Daikin says to notify the installer and report the error code. Some codes can be reset with the ON/OFF button, depending on level, but a code that returns means the cause is still there.
  4. Clean what users may clean. Daikin says the end user may clean the air filter, suction grille, air outlet and outside panels, with the unit turned off. Its rule of thumb is every six months, more often if the air is extremely contaminated.
  5. Look, but do not open up. The same manual says never to inspect or service the unit yourself. Ceiling-void panels, drain pans and pumps are for a qualified person.

What does an engineer check?

The tests installers use to prove a new drain show the method. Daikin's manual says to pour about one litre of water through the discharge outlet or water inlet and check for leaks, and describes a service drain outlet with a rubber plug for emptying the pan. Mitsubishi's says to confirm the drain-up mechanism runs and the connections stay dry, using a transparent hose to see the drain discharge. An engineer investigating a leak can repeat that, then work back through the fall, the pump and the insulation.

Where the cause is ice, low charge or another refrigerant-side fault, the work breaks into the circuit, which REFCOM counts as maintenance or servicing and Article 3 of Regulation (EU) No 517/2014 says must be done by a certified undertaking. The guide to checking an F-gas certificate shows how to confirm the company and the engineer. The commercial air conditioning repair page explains how callouts are diagnosed. Drain and pump design for retrofits is in the condensate pumps and drains guide, and odours from standing condensate are in the air conditioning smells guide. Readers who want a contractor to look at a recurring leak can send an enquiry through the site's form.

What are the risks of leaving it?

The first is a fall. HSE says the Workplace (Health, Safety and Welfare) Regulations 1992 require floors to be suitable and in good condition, and employers must assess slip and trip risks under the Management of Health and Safety at Work Regulations 1999. The second is damage: Daikin links a badly connected drain hose to damage to the installation space and its surroundings.

Legionella needs proportion. HSE's test for a reasonably foreseeable risk includes a system that creates or spreads breathable droplets and one that stores or recirculates water, and it says all systems need a risk assessment but not all need elaborate control measures. Whether a condensate tray features in a site's assessment is for the dutyholder; the air conditioning and legionella guide explains where air conditioning appears in one.

Sources

Common questions

Does dripping water mean the refrigerant is low?

Not by itself, because most drips are drainage or insulation faults. Ice formation and insufficient cooling capacity are listed as grounds to suspect a refrigerant leak, so a dripping unit that also ices or cools poorly needs an F-gas engineer.

Is it safe to keep a dripping unit running?

Daikin's table says to stop operation when water leaks from the unit, and warns elsewhere that a wet indoor unit risks electric shock or fire. Stop the unit, contain the water and arrange a check.

Can staff reset a drain fault code?

Daikin says that, depending on the level of the code, it can be reset with the ON/OFF button, and otherwise to ask the installer for advice. A code that comes back means the cause remains, so report it with the unit details.

Why do drips appear in humid weather?

Daikin's operating-range note says its humidity limit is there to avoid condensation and water dripping out of the unit. Past the limit, safety devices may operate, so persistent drips in humid spells are worth raising with the installer.

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