A condensate pump is a small pump and float switch that lifts the water an air conditioner collects up and away to a drain. Daikin and Mitsubishi Electric ceiling cassettes have one built in, and Daikin states lifts of 580 to 675 mm on the cassettes covered below.
Picture a Monday morning. The ceiling tile under the cassette is stained, or the unit has stopped and the remote is showing a code, and it was fine on Friday. Somebody has already put a bin underneath and asked whether it is the pump or the pipe.
At a glance
| Question | What the manufacturer manuals say |
|---|---|
| Is the pump built in? | Daikin FXZQ15 to 50A2VEB: "The indoor unit is equipped with a built-in drain pump and float switch." |
| What does a tilted unit do? | If the drain piping side is raised, "the float switch may malfunction and cause water to drip" (Daikin FXZQ15 to 50A2VEB). |
| What fall does the drain pipework need? | "Make sure the drain piping slopes down (at least 1/100)" (Daikin FCAG35 to 140BVEB). |
| How high can the pipe rise after the unit? | Rising piping: "≤300 mm from the unit, ≤675 mm perpendicular to the unit" (Daikin FCAG35 to 140BVEB). |
| What about the hose at the unit? | Drain hose inclination of "0~75 mm to avoid stress on the piping and to avoid air bubbles" (Daikin FCAG35 to 140BVEB). |
| How is the drain tested? | Gradually pour approximately 1 l of water through the air discharge outlet and check for leaks (Daikin FCAG35 to 140BVEB). |
Source: Daikin FXZQ-A installation and operation manual and Daikin FCAG-B installation and operation manual
Why an air conditioner makes water, and where the pump sits
Cooling air also dries it. Moisture in the room condenses on the cold coil, drips into a drain pan and has to go somewhere. If the unit sits high on a wall and the pipe can fall away to a drain by gravity, nothing more is needed. A ceiling cassette sits in the void with very little height to play with, so the water often has to travel uphill first, and that is the pump's job.
On Daikin's UK range the picture is consistent. The FXZQ-A fully flat cassette lists a "Drain pump kit (standard)". On the FXAQ-A wall mounted unit the same line reads "(optional)". On that wall unit the pump is an option rather than a standard part. Our post on split versus cassette air conditioning explains why cassettes lean on pumps more.
The pump is only half of the system. The float switch in the drain pan tells the unit when the water level is too high, and the pump, the float switch and the pipework have to agree with each other. When one of them is wrong, the first sign is usually water, a stopped unit or a noise.
Symptoms, likely causes and who does what
The table below keeps to what the manuals say. It sets out a safe first look and where the engineer takes over. Our post on air conditioning leaking water covers the wider list of leak causes that have nothing to do with the pump.
| Symptom | Likely cause (from the manuals) | Safe check | Engineer job |
|---|---|---|---|
| Water dripping from the unit | Unit tilted so the drain side is raised, so "the float switch may malfunction and cause water to drip" (Daikin) | Look for a unit or panel that has dropped or sits visibly out of level. Do not touch the float switch | Re-level the unit and test the float switch |
| Draining or motor sound after the unit is switched off | Mitsubishi Electric: "When cooling operation stops, the drain pump operates and then stops" | Wait approximately 5 minutes, as the manual says | Only if the sound carries on beyond that |
| Unit stops and shows a drain code | For the Mitsubishi Electric PLA-M35 to 140EA2, P4 is "Drain sensor error/Float switch connector open" and P5 is "Drain pump error" | Note the code and model. The manual says "Turn off the power switch immediately and consult your dealer" | Test the pump, float switch and connector, and clear the drain line |
| Abnormal sound when the pump stops | Daikin: if air stagnates in the hose, "the drain may flow oppositely when the drain pump stops and generate abnormal sound" | Note whether the sound comes when the pump starts or stops | Check the hose is level or slightly upgraded and the riser height |
| Slow draining, standing water or a musty smell | Daikin: "If water stagnates in the drain piping, it may cause clogging of drain piping" | Look for sagging pipe runs you can see from below | Flow test with water and a check of the fall |
Source: Daikin FXCQ-A installation manual and Mitsubishi Electric PLA-M.EA operation manual. The P4 and P5 code meanings are from the PLA-M35 to 140EA2 installation manual linked under the next table, and the tilt row is also in the Daikin FXZQ manual cited above.
What the manufacturers publish for pump lift
Every maker states a lift for the built-in pump, and it matters because it caps how high your drain route can rise above the unit. Pump lift is not a number to improvise. If the route needs more than the pump is rated for, the water does not arrive.
| Model range | Type | Pump | Stated figure |
|---|---|---|---|
| Daikin FXCQ-A | 2-way blow ceiling mounted cassette | Drain pump kit (standard) | "Standard drain pump with 580mm lift" |
| Daikin FXZQ-A | Fully flat cassette | Drain pump kit (standard) | "Standard drain pump with 630mm lift" |
| Daikin FCAG-B | Round flow cassette | Standard drain pump | Drain pump with 675mm lift |
| Daikin FXAQ-A | Wall mounted unit | Drain pump kit (optional) | No lift figure on the product page |
| Mitsubishi Electric PLA-M35 to 140EA2 | Ceiling cassette | Drain pump and float switch (check codes P4, P5) | Drainage figure marks a raised section "Up to 85 cm", with a downward slope of 1/100 or more |
Source: Daikin UK product pages (FXCQ-A, and the FXZQ-A, FCAG-B and FXAQ-A pages on the same site) and the Mitsubishi Electric PLA-M35 to 140EA2 installation manual
The figures are not interchangeable between ranges, and they are not the same as the total height of your drain route. Always read the one for your model. Daikin's FXCQ manual gives the same 580 mm as the maximum height of the drain riser and then adds something people do not expect: "the higher the drain riser the lower the draining noise. Therefore, the drain riser of 300mm or higher is recommended." A pump forced to push through a very low riser can be the noisy one.
Falls, risers and the pipework after the pump
A pump fault is often partly a pipework fault. The manuals are specific on the geometry, and they agree on the basics. The pipe has to fall away from the unit, at least 1/100 in both the Daikin FCAG-B and Mitsubishi Electric PLA-M manuals. Any rise has to be close to the unit. And the unit itself has to be level, because the float switch is sensitive to that.
The Daikin FCAG-B manual puts the rise at "≤300 mm from the unit, ≤675 mm perpendicular to the unit". The FXCQ manual adds "keep the drain hose level or make a slight up-grade so that air may not stagnate in the drain hose". It also says: "Do not apply external force to the float switch. (It may result in malfunction)". That last line is a good reason not to poke at the pan with a screwdriver to see what happens.
What you can safely check
- Switch the unit off at the remote and note the model and any code on the display before you do anything else.
- Look for a visibly sagging ceiling panel or tile under the unit, and check whether the grille sits flush.
- Wait about 5 minutes after the unit stops, as Mitsubishi Electric's manual says, before deciding a pump sound is a fault.
- Check the clear section of the drain hose, where there is one, for standing water.
- Do not open the unit, touch the float switch or pour water into the pan. That is the engineer's test.
A planned service is where drain lines should be looked at before they fail. If you are writing a maintenance specification, what to specify in an air conditioning maintenance contract is worth reading, and drain pump and float switch checks belong on the list.
When to call an engineer
Water is falling into a ceiling void and a unit has stopped on a drain code. The pump, float switch and pipework all need testing together, not one at a time. Be Cool is a family-run London firm with F-Gas certified engineers, trading since 2004, and we handle air conditioning repair across London and the South East, including 24/7 emergency callouts.
Frequently asked questions
Do all air conditioners have a condensate pump?
No. Daikin lists the drain pump kit as standard on its FXCQ-A and FXZQ-A units and as optional on its FXAQ-A wall unit. Where the pipe can fall to a drain by gravity, no pump is needed.
How high can a built-in drain pump lift water?
It depends on the model. Daikin states 580 mm for the FXCQ-A, 630 mm for the FXZQ-A and 675 mm for the FCAG-B. Check the manual for your own unit.
Why does my pump keep running after the unit stops?
Mitsubishi Electric's manual says that when cooling stops, the drain pump operates and then stops, and to wait approximately 5 minutes. If it never stops, have it checked.
What does a drain alarm on the remote mean?
On the Mitsubishi Electric PLA-M35 to 140EA2, P4 is "Drain sensor error/Float switch connector open" and P5 is "Drain pump error". Codes differ by manufacturer and range, so use the manual or an engineer for your own unit.
Is a noisy condensate pump a fault?
Not always. Daikin notes that a low drain riser makes the pump louder and recommends 300 mm or higher, and trapped air in the hose can cause an abnormal sound when the pump stops. A new noise that was not there before deserves a look.
Fix the drain before the ceiling tells you
A drain fault often traces back to level or pipework as much as to the pump, and a quiet weekend is when it shows up as a stain on the ceiling. Manufacturer figures and codes change between ranges, so these are the manuals as of October 2026, and your own unit's manual always wins.
About the author: Ali Elm runs Be Cool Refrigeration & Air Conditioning, a family-run London firm that has been installing, servicing and repairing commercial refrigeration and air conditioning since 2004. His F-Gas certified team has delivered more than 2,000 projects across London and the South East.
Last updated: 30 October 2026
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.