This is the most common reason for a leak. As your AC cools your home, it pulls humidity out of the air. That moisture turns into water and should flow down a plastic drain line.

• • The Problem: Over time, dust, algae, or even Calgary’s mineral-rich water can cause a sludge buildup in the pipe. When the line clogs, the water backs up and overflows the internal drain pan.

  • The Fix: You can sometimes clear a clog using a wet/dry vacuum to suck the blockage out from the outside end of the pipe. If the backup is severe, a professional flush is required.

If you have an older AC unit (10+ years), the secondary drain pan—the tray that catches condensation—might be reaching the end of its life.

• • The Problem: Metal pans can rust through, and plastic pans can crack over time. Even a tiny pinhole leak will eventually lead to a puddle on your basement floor.

  • The Fix: Check the pan with a flashlight. If you see rust spots or cracks, the pan needs to be replaced.

It might seem strange to find ice inside a machine during a Calgary heatwave, but it happens more often than you’d think.

• • The Problem: If your AC has restricted airflow (usually from a dirty air filter) or is low on refrigerant, the coils can drop below freezing. The humidity in the air turns to ice on the coils. When that ice eventually melts, it’s more water than the drain pan can handle, causing a flood.

  • The Fix: Turn your AC off immediately to let it thaw. Change your air filter and check for any blocked vents in your home.

If your AC is located in a basement where the water can’t drain by gravity, you likely have a condensate pump to push the water up and out of the house.

• • The Problem: If the pump motor fails or the float gets stuck, the water has nowhere to go but out onto your floor.

  • The Fix: Check if the pump is plugged in and receiving power. If it’s humming but not moving water, the pump likely needs to be replaced.

If your AC was recently installed and it’s already leaking, it might not be level.

• • The Problem: AC units and their drain pans are designed to be slightly tilted toward the drain. If the unit was installed unevenly or has shifted on its base, the water will spill over the “low side” of the pan instead of entering the drain line.

  • The Fix: A professional technician can re-level your unit to ensure proper drainage.