Why is My Aircon Leaking Water? Whether it’s a sweltering July afternoon or a humid September morning in the UK, your air conditioning unit is your home’s best friend. But that friendship can feel a little strained when you notice a puddle forming on the floor or a steady drip coming from the indoor unit.

At OJ Gas & Heating, we see this frequently. While a leaking aircon is a common headache, it isn’t something you should ignore. Left untreated, a small drip can lead to serious water damage to your walls, ruined flooring, or even electrical faults.

Here are the 5 most common reasons your aircon is leaking water and what you can do about it.

1. The Blocked Condensate Pipe

The most frequent culprit is a simple blockage. Your aircon doesn’t just cool the air; it dehumidifies it. That moisture turns into liquid and travels through a narrow pipe to the outside. Because this pipe is damp, it can attract dust, sludge, or even small insects. Once the path is blocked, the water backs up and spills out of the internal unit’s drainage tray.

2. Frozen Evaporator Coils

It sounds counterintuitive, but if your aircon gets too cold, it will leak. If the airflow is restricted, usually by a very dusty filter, the refrigerant coils can drop below freezing and turn into a block of ice. When you eventually turn the unit off, that ice melts rapidly, overwhelming the drainage system and resulting in a puddle on your floor.

3. Refrigerant Gas Leaks

Your system relies on a specific “charge” of refrigerant gas to operate. If there is a small hole or a loose joint in the copper piping, the pressure drops. This imbalance causes the cooling coils to freeze over (much like the airflow issue mentioned above). If you notice a “hissing” sound or the air isn’t feeling as cold as it should, a gas leak is the likely suspect.

4. A Damaged Internal Drain Pan

Inside the unit, directly beneath the cooling coils, sits a tray designed to catch every drop of condensation. In older systems, these trays can develop tiny cracks or suffer from corrosion. Even a hairline fracture in this plastic or metal pan will allow water to seep through the internal casing of the unit and drip down your wall.

5. Faulty Condensate Pump

In some UK homes, especially in flats or basement conversions, the aircon cannot rely on gravity to drain the water away. Instead, a small “condensate pump” is used to push the water up and out. Like any mechanical part, these pumps can burn out or lose power. If the pump fails, the water stays trapped in the unit until it inevitably overflows.

Prevent Water Damage with OJ Gas & Heating

While cleaning a filter is a great DIY task, most leaks involve internal components that require a professional touch. Ignoring a leak doesn’t just ruin your wallpaper; it can lead to mould growth inside the unit and permanent damage to the electronics.

Why choose OJ Gas & Heating?

  • F-Gas Certified: We are legally qualified to handle all refrigerant and gas-related repairs.
  • Local Expertise: Serving South London and the surrounding areas with honest, transparent pricing.
  • Comprehensive Servicing: We don’t just fix the leak; we clean and optimise your system to lower your energy bills.