What the Drain Pan Does and Why It Overflows
Every heat pump that cools your home produces condensate, and the drain pan sits directly under the indoor coil to catch it. From there, water flows out through a drain line. The pan is meant to stay nearly empty — it's a catch basin, not a reservoir. When you find it full or spilling over, water is arriving faster than it can drain away.
There are really only two ways that happens: either the drain can't carry the water off (a blockage or bad slope), or the coil is producing far more water than normal (a freeze-and-thaw cycle). On ducted systems common in Greater Vancouver, there's often a primary pan built into the coil and a secondary backup pan below it, sometimes with a float switch to shut things down before water reaches your ceiling.
An overflowing pan is not something to wait out. The water it releases lands on framing, drywall, flooring, or the equipment itself, and it invites mold. Acting quickly limits the damage.
Clogged Drain Lines: The Number-One Cause
By far the most common reason a pan overflows is a clogged condensate drain. The drain line, and the P-trap on ducted systems, gradually fill with algae, dust, and biofilm. Once the passage closes, condensate has nowhere to go and the pan backs up.
The outdoor end of the line is just as likely to block. In Vancouver, drain outlets get plugged by leaves, garden debris, insect nests, or a slug of winter ice. If the exit is sealed, the entire line backs up to the pan.
Slope is the quieter culprit. Condensate drains rely on gravity and must fall continuously toward their exit. A line installed flat, or one that has sagged into a belly over the years, holds standing water and overflows even when it's clean. A technician clears the blockage, flushes the line, and verifies the slope so it actually carries water away.
Frozen Coils and Failed Pumps
When the drain is clear but the pan still overflows, the cause is usually too much water, too fast — and that means a frozen coil. If the system is low on refrigerant or starved for airflow, the coil ices over. When it thaws (often after the unit cycles off), the ice melts in a rush that overwhelms even a clean drain. Low refrigerant typically comes with weak cooling and a unit that runs nonstop; that's a sealed-system problem for a licensed tech, since refrigerant work is regulated in BC.
The most preventable trigger for a freeze is a dirty air filter, which chokes airflow across the coil. Cleaning or replacing the filter on schedule heads off most freeze-driven overflows.
On installs that can't drain by gravity — common in Vancouver basements and interior closets — a condensate pump lifts the water out. If the pump fails or its float switch sticks, the pan overflows quickly even though everything else is fine. A stuck float switch can also falsely shut the system down, which is a clue worth mentioning when you call.
Stop the Damage, Then Call CanroHeat
When you find an overflowing pan, act fast but stay safe. Turn the system off at the thermostat or remote so it stops adding water. Mop or vacuum the standing water and protect anything below the unit. Check and clean the air filter if it's dirty. If you can reach the drain's outdoor exit, clear away any debris or ice blocking it. A wet/dry vacuum on the outdoor end of the drain can sometimes pull a clog free.
Don't open the coil cabinet, dismantle a condensate pump, or touch the refrigerant circuit — those need proper training and tools, and refrigerant handling is regulated. If your system shut itself off via a float switch, leave it off until it's serviced; that switch is protecting your home.
Heat pumps are serviced by our parent company, CanroHeat. For an overflowing pan that won't clear, call 604-359-1081 and we'll find the cause and fix it before it does real damage.
Repair Costs and Prevention in BC
Cost depends on what's behind the overflow, so here are broad ranges. Clearing a clogged drain and trap, flushing the line, and treating the pan is normally the most affordable visit. Re-sloping a drain, replacing a cracked pan, or swapping a failed condensate pump or float switch falls in the mid range with parts added. Refrigerant-related freeze problems vary the most and can't be quoted without inspecting the system.
The best prevention is cheap: clean the filter monthly in cooling season, and have the drain line cleared and the system checked once a year. Annual maintenance catches a building clog or a low refrigerant charge before it floods your pan.
For a precise quote, or to set up annual maintenance, call CanroHeat at 604-359-1081. We diagnose the overflow, explain the cause, and quote the fix before starting.