Condensate pump
A small pump that lifts condensate from an indoor unit or a condensing appliance up to a drain it cannot reach by gravity. It works against a maximum lift stated in the installation manual, and a level switch alongside it stops the equipment before the collection tray can overflow.
Also called condensate lift pump, drain pump
What is a condensate pump for?
A condensate pump lifts water from a cooling coil or a condensing appliance to a drain above it. Its allowed lift is set by the installation manual, and a level switch stops the equipment if the water is not leaving fast enough.
Condensate pump: how it works
Water collected in the tray reaches a level that starts the pump, which discharges it through a small-bore pipe to a gravity drain. Because the pump has a stated maximum lift and the pipe that follows needs a minimum fall, the arrangement is a property of the installation rather than of the appliance. When condensate arrives faster than it leaves, the level rises to the switch and the equipment stops.
Where you meet the term
- On a ceiling cassette, where there is no route for gravity drainage from a unit set into a ceiling void.
- On a condensing boiler or furnace in a basement, where the drain point sits above the appliance.
- In a drain protection code, where the pump, the level switch, and the pipe run are all inside one reported condition.
How to check it
- Watch the external drain point during cooling. A unit that has been producing condensate should discharge water outside. A dry discharge during humid weather says the water is not leaving, whatever the pump is doing. Owner check
- Listen for the pump running. Many pumps are audible as a brief buzz at intervals during cooling. A pump you can hear that produces no discharge is a different report from one that never runs. Owner check
- Measure the lift and fall against the manual. The installed lift and the fall of the gravity run that follows are compared against the values the installation instructions allow, which is where marginal installations are found. Technician
Condensate pump: what it is not
- A drain protection code is not proof the pump has failed. A lost gradient, an air lock, or a restricted inlet leaves a working pump unable to keep up.
- A condensate pump is not a sump pump. Its capacity is small, its lift is limited, and it is sized for the condensate rate of one appliance rather than for water in bulk.
Condensate pump questions
How high can a condensate pump lift water?
Each pump has a maximum lift stated in its own literature and in the appliance installation instructions. Exceeding it produces intermittent drain faults that look like a failing pump but are an installation matter.
Why does my cassette leak even though the pump works?
Water can arrive faster than a marginal arrangement removes it, particularly in humid weather. The pump running and the tray emptying quickly enough are two different things.
Can I clean a condensate pump myself?
The pump sits inside the indoor casing alongside the board and the fan supply on most equipment, so access is service work rather than owner maintenance.
Where this definition comes from
Written from manufacturer support article material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- Mitsubishi Electric P5 diagnostic referenceMitsubishi Electric fault-code reference assigning P5 to a drain pump or drain overflow protection detection on the indoor unit, naming the drain pump circuit, the float switch, and the condensate path as the checked elements, and scoping the entry to the families that publish the P-series table.
- Troubleshooting the HVAC air handler overflow switchTrane residential page on the condensate overflow switch: it may be installed on the inside or the outside of the drain pan, it is not fitted to every air handler and can be added later, and on a trip it shuts down the outdoor compressor and condenser fan and the supply fan so no further condensate is produced; blockage is attributed to dirt, debris, mould growth or spider webs in the pan or line.