Home / Services / Condensate Pump Replacement
Heating & Cooling · DrainageCondensate Pump Replacement
Condensate pump replacement costs $250–$450 installed and takes about an hour: the failed pump comes out, a new one goes in with a fresh discharge tube, and its overflow switch is wired to shut the furnace or AC off before the reservoir can spill. Pumps are sealed units, so a seized motor or a failed float switch means a new pump, not a repair. If yours is overflowing now, switch the furnace or AC off at the thermostat and the equipment stops making water.
A condensate pump is needed whenever the water cannot drain by gravity. A condensing furnace, an AC coil and a condensing tankless water heater all produce water, and it has to reach a drain. If there is no floor drain near the equipment, or the nearest drain, laundry sink or standpipe sits higher than the unit's outlet, a small pump collects the water in a reservoir and lifts it there through a narrow vinyl tube. Finished basements in 2000s+ houses, furnaces moved during a renovation, and AC added to an older home whose only floor drain is across the room are the usual cases.
Pumps fail in four ways. The float sticks, glued down by the grey-brown slime that grows in condensate, or the motor seizes and hums without moving water. The check valve at the outlet stops sealing, so every pumped load runs back into the reservoir and the pump short-cycles until it burns out, or the discharge tube plugs with the same slime. Each of them ends the same way: a full reservoir, then water across the floor and under the furnace.
The detail that prevents the flood is the safety switch. Most pumps have a second float with two low-voltage leads that open when the water rises too high, and wired in series with the thermostat circuit they stop the furnace or AC before the reservoir overflows. It is common to find those leads coiled up and never connected. On a condensing furnace we also fit a neutraliser ahead of the pump: furnace condensate is acidic enough to etch concrete and corrode cast-iron drains, and a cartridge of calcite media raises its pH before it goes down the drain.
Where the discharge goes matters as much as the pump. The tube should run to an indoor drain with an air gap; a line run outdoors will freeze in the first cold week and back the water up into the furnace — see a frozen furnace condensate line. In summer the same pump handles the AC coil, and on humid days near Lake Ontario that is many litres a day. A pump that has started to hum, rattle or run constantly is warning you before it floods, so book the replacement then.
Replace the condensate pump when
- Water is pooling around the furnace or the pump reservoir is full to the brim
- The pump hums or buzzes but the water level does not drop
- It runs every minute or two — the check valve is letting water fall back
- The furnace or AC shuts off and only restarts after you empty the reservoir by hand
- The reservoir is cracked, slime keeps fouling the float, or the pump has already been through one overflow
How it works
Water under a furnace can also come from a clogged trap, a cracked drain pan or a humidifier. The technician pours water into the reservoir to see whether the float, motor and check valve respond, and checks the trap and drain line upstream.
The old pump and its slimed tube come out. The new pump is set level, the discharge is run to an indoor drain with a proper air gap, and on a condensing furnace a neutraliser goes in line.
The overflow switch is wired into the thermostat circuit, then tested by filling the reservoir until it trips and confirming the equipment stops. You see it work before we leave.
Common questions
How long does a condensate pump last?
It varies with how hard it works and how dirty the water is. A pump serving only an AC coil runs a few months a year; one serving a condensing furnace, an AC and a humidifier runs year-round and handles acidic water. Flushing the reservoir once a year during a tune-up extends its life. Once the motor is noisy or the float sticks repeatedly, replace it before the heating season, not during it.
Can I replace a condensate pump myself?
The plumbing side is simple: a plug-in pump, a tube and a drain. The part that gets skipped is the safety switch, which ties into the furnace's 24-volt control wiring, and a wrong connection can blow the control board fuse or leave the furnace running through an overflow. If you fit one yourself, have the cut-out wired and tested on your next service visit.
Why does my pump keep running or cycling?
A pump that starts every minute or two has a leaking check valve: the water it just lifted falls back down the tube and refills the reservoir. A pump that runs without stopping has a stuck float or a blocked discharge. Both wear the motor out quickly. Why a condensate pump overflows covers what to look at first.
Do I need a neutraliser?
For a condensing furnace or a condensing tankless water heater we recommend one, especially where the water runs to a cast-iron drain or across a concrete floor to reach it. AC condensate is not acidic and does not need it. The cartridge's media is used up slowly as it works, so it gets checked and topped up or replaced at the annual service.
Is it the pump or the furnace that is leaking?
Look at where the water starts. A full pump reservoir with a silent motor points to the pump; a dry reservoir with water coming from inside the furnace cabinet points to a blocked trap, a cracked collector box or a loose hose. The second group is furnace repair, and why a furnace leaks water sorts the causes.