Condensate pump not working
If your furnace or air handler sits in a basement, an attic. Or anywhere a drain line can't run downhill to daylight, it almost certainly uses a condensate pump. When that pump fails, it either leaks or it shuts the whole system down, and the fix depends on which one is happening.
What a condensate pump actually does
Not every furnace or air handler can drain by gravity to a floor drain or outside. When the unit sits below floor level, in an attic, or anywhere a straight downhill run isn't possible, a condensate pump takes over. It's a small reservoir with a float switch and a motor that pushes the water up and out through a thin discharge tube. That makes it a mechanical device with moving parts, not a passive pipe, which is exactly why it fails in ways a plain drain line doesn't.
Is it actually leaking, or is the reservoir just full?
Look at where the water is coming from before assuming the worst. Water sitting inside the pump's reservoir box, right up near the rim, usually means the pump isn't pumping, not that the box is cracked. Water on the floor around the outside of the box. Or dripping from a seam in the housing, points instead to a physical failure of the box or a loose fitting. These are two different repairs, so check which one you actually have before doing anything else.
The float switch is stuck, or the motor has failed
Inside the reservoir, a small float rises with the water level and triggers the pump's motor once it reaches a set point. If that float is stuck, jammed by mineral buildup or debris, the pump never turns on no matter how full the box gets.
A motor that has simply worn out or seized shows the same symptom from a different cause: the float moves freely, but nothing happens. You can usually tell them apart by watching the float by hand. Lift it gently and listen for the motor. Silence points to the motor; a motor that runs but doesn't move water points somewhere else in the system.
The discharge tube is blocked, kinked, or disconnected
The thin tube that carries pumped water away is often just pushed onto a barbed fitting, not glued. So it can slip loose behind a unit nobody looks at often. Algae and sediment can also narrow it over time, the same way they narrow a gravity drain line. Say the pump runs constantly, or cycles on and off rapidly, but never actually gets the water level down. It is usually fighting a blocked or disconnected tube rather than a failed motor.
The check valve is missing or installed backward
Many condensate pumps use a small check valve on the discharge line so pumped water can't flow back into the reservoir between cycles. A missing check valve, or one installed facing the wrong direction, lets water drain right back down after each pump cycle. The float never stays low, and the pump seems to run nonstop without making progress. It's a small part, and one of the more overlooked reasons a pump that is otherwise working still can't keep up.
Your system may be shutting itself off, and that's on purpose
Most condensate pumps wire into a safety switch that cuts power to the furnace or air conditioner the moment the reservoir gets dangerously full. If your system has simply stopped running, with no other symptom, a tripped condensate switch is one of the least dramatic and most common explanations. It is doing exactly what it was built to do: stopping the system before an overflowing pump box turns into water damage.
What's reasonable to check yourself
| What to check | What it usually means |
|---|---|
| Is the pump plugged in and getting power? | A pump unplugged during other work is more common than it sounds |
| Does the float move freely when lifted by hand? | A stuck float means the pump never gets the signal to start |
| Is the discharge tube kinked, disconnected, or visibly clogged? | Water has nowhere to go even if the motor is running fine |
| Does the motor hum or run but the water level doesn't drop? | Points to a missing or backward check valve, or a worn-out pump mechanism |
What not to do
- Don't bypass or disable the safety switch to force the system back on. It exists to stop water damage, and defeating it removes that protection entirely.
- Don't ignore standing water in or around the unit while you wait to see if it dries out on its own. It rarely does, and delayed water intrusion damages flooring and drywall.
- Don't open the pump's electrical housing or rewire its connections yourself. If the motor itself has failed, that's a repair or replacement for a technician, not a homeowner electrical project.
Why is my condensate pump running but not pumping?
A pump that runs but does not lower the water level is usually fighting the discharge line, not a dead motor. Check the thin discharge tube first. It is often only pushed onto a barbed fitting, so it can slip loose, kink or narrow with algae and sediment.
The next suspect is the check valve. If it is missing or installed backward, water drains straight back into the reservoir after each cycle, so the pump seems to run nonstop without making progress.
If the float moves freely and the motor hums but nothing moves, a worn-out pump mechanism is also possible. Do not bypass the safety switch, and leave the electrical housing to a technician.
Condensate pump symptoms and what each one points to
Short answer: watch what the pump does, then match it to a cause. The pattern of the failure tells you more than the water on the floor. This table pulls together the causes explained above.
| What you see | Most likely cause | Your next step |
|---|---|---|
| Reservoir full to the rim, pump silent | Stuck float or a failed motor | Lift the float gently and listen; silence points to the motor, which is a job for a technician |
| Pump runs constantly or cycles fast, level stays up | Blocked, kinked or disconnected discharge tube | Check that the tube is still on its barbed fitting and not kinked |
| Pump runs nonstop and water flows back after each cycle | Missing or backward check valve | Have the check valve looked at |
| Motor hums, float moves, nothing drains | Worn-out pump mechanism | Repair or replacement by a technician |
| Water on the floor outside the box, or a dripping seam | Cracked box or loose fitting | Dry the area and get it repaired |
| System stopped with no other symptom | Tripped condensate safety switch | Find out why the reservoir filled; never bypass the switch |
If your unit has no pump and drains by gravity instead, the causes are different: read the guide to a clogged condensate drain line. Leave the pump's electrical housing closed in every case.
Frequently asked questions
Can I just unplug or bypass the safety switch to stop the system from shutting off?
No. That switch exists to stop the system before an overflowing pump causes water damage, and defeating it removes that protection entirely. If the system keeps shutting off, the pump needs to be fixed, not the switch disabled.
Is this the same problem as a clogged condensate drain line?
No, even though the symptom can look similar. A drain line problem is a blocked pipe relying on gravity. A pump problem involves a motor, a float switch, and a check valve, and fails in different ways. If your system doesn't use a pump at all, see the article on a clogged condensate drain line instead.
How do I know if my system even has a condensate pump?
Look near the indoor unit for a small box with a thin tube running out of it, usually toward a wall or a window. If your system instead drains straight down into a floor drain or a line that runs outside, it doesn't use a pump, and a different set of causes applies.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- US EPA. Improving Indoor Air Quality
- US EPA. Introduction to Indoor Air Quality