Why isn't my condensate pump working?
Updated August 2026
A condensate pump that has gone quiet or is overflowing is usually a stuck float or a reservoir clogged with slimy gunk, so the pump never gets the signal to run or cannot move the water it collects. These small pumps sit under a high-efficiency furnace, an AC, or a mini-split and fill with algae and dust over a season. Cleaning the reservoir is free and fixes most cases, while a worn-out pump is a $50 to $150 replacement. Work through the checks below before you buy a new one.
Safety first: the pump is the last thing standing between your AC or high-efficiency furnace and a floor full of water, so a working overflow safety float matters. Wire the pump's safety switch so it shuts the HVAC system off when the water rises too high; without it, a failed pump simply overflows onto the floor or the ceiling below. The pump runs on line voltage right next to standing water, so unplug it before you clean the reservoir, and if it shares a GFCI outlet, a trip there is often what killed it.
Causes, most likely first
| Cause | How likely | The fix | Typical cost |
|---|---|---|---|
| Stuck float switch | Most common | Sludge or a tilted pump leaves the float jammed down (pump never runs) or up (runs dry). Clean it and free the float. | Free |
| Clogged reservoir or intake | Common | Algae and dust turn to sludge that blocks the pump inlet. Unplug it, pour out the muck, and flush the tank clean. | Free (a $5 brush) |
| Blocked or kinked discharge line | Common | The vinyl tube that lifts the water is clogged, crimped, or airlocked. Clear it and confirm it drains uphill freely. | $0–75 |
| Burned-out pump motor | Occasional | The float rises but nothing hums, or it buzzes without pumping. The motor has failed and the whole pump gets swapped. | $50–150 |
| No power to the pump | Occasional | The pump is unplugged, on a tripped outlet, or its GFCI has popped. Restore power and reset the outlet. | $0 |
Check these first
- Confirm the pump is plugged in and the outlet has power, then test and reset the GFCI it may be on.
- Lift the float by hand with the pump powered. It should kick on and pump; if it hums but no water moves, the impeller or discharge line is blocked.
- Unplug the pump, pop the lid, and look inside for sludge, algae, or slime clogging the reservoir and the float.
- Trace the clear discharge tube for a kink, a sag holding water, or a clog at the far end where it drains.
- Pour a cup of water into the reservoir to trigger the float, and watch whether the pump evacuates it or overflows.
Prevent it next time
Condensate pumps fail from neglect more than age, and a quick seasonal cleaning prevents nearly all of it. Flush the reservoir and check the float on the recommended cleaning schedule, ideally at the start of cooling season, and drop a condensate pan tablet in to slow the algae. If you are not sure which part of your system this even is, our explainer on what a condensate pump does shows where it sits and why it matters. A pump lasts only a few years of hard use, so budget $50 to $150 to replace one that is buzzing or worn rather than waiting for the overflow.
When to call a pro
Cleaning the reservoir and clearing the discharge line are easy DIY wins, and swapping a $50 to $150 pump is within reach if you can match the fittings and the lift height. Bring in an HVAC tech when the pump is clean and powered but still will not run, when the safety float is not wired to shut the system down, or when water keeps appearing despite a working pump, since the leak may be upstream at the coil or drain pan. A service call runs $75 to $200. Do not just keep emptying the reservoir by hand, because the moment you forget, it floods.
Most of the causes above are maintenance problems wearing a disguise. OnOtto keeps the boring prevention on schedule so the 2 a.m. version doesn't happen.
Stop chasing symptoms, free for 30 daysFrequently asked questions
How do I clean a condensate pump?
Unplug it first, then lift the pump out and pour the dirty water into a bucket. Remove the top or the pump body, wipe the sludge from the reservoir walls and the float, and clear the small inlet screen. Mix a weak bleach-and-water or vinegar solution, swish it through the tank and the discharge tube to kill algae, then rinse. Reassemble, pour in clean water to test the float and flow, and drop in a pan tablet to slow regrowth. The whole job takes 15 to 20 minutes.
Why is my condensate pump full of water and not draining?
Either the float is stuck down so the pump never starts, or the pump runs but cannot push water out. Lift the float by hand: if the motor kicks on, the float was jammed by sludge and a cleaning fixes it. If it hums but the water level does not drop, the impeller is clogged or the discharge line is blocked or airlocked. A pump that sits silent and dead with a raised float has usually burned out and needs replacing for $50 to $150.
What happens if my condensate pump stops working?
The water it was lifting has nowhere to go, so the reservoir overflows onto the floor or backs up into the furnace or AC drain pan. If the pump has a safety float wired to the HVAC system, the equipment shuts off before it floods, trading cooling or heat for a dry floor. Without that safety, you get water damage, and a pump under an attic air handler can leak straight through a ceiling. That is why the safety float and a seasonal cleaning are cheap insurance against a four-figure repair.
How long do condensate pumps last?
Typically three to seven years, less if they are never cleaned. They run every cooling cycle, sit full of damp, algae-friendly water, and use a small motor that wears out, so they are one of the shorter-lived parts on an HVAC system. Cleaning the reservoir each season and keeping the discharge line clear stretches their life toward the top of that range. When one starts buzzing, cycling oddly, or leaking at the seams, replace it for $50 to $150 before it fails during a heat wave.