Furnace Condensate Pump Installation & Repair

Today you’re going to learn how to check and replace a condensate pump on your furnace. Why? Because last month I went down into my basement and found a big puddle of water under my furnace. And when I have to fix things in my house, you get to learn how to fix them in yours.

By the size of the puddle I’d say the pump had gasped its last breath about a week earlier and it was time to hold a funeral for my sputtering Little Giant pump.

If you live in an older home that doesn’t have a drain in the basement you probably have a condensate pump. And like any small appliance there’s gonna come a time when it breaks down.

You will get angry at it, probably get upset that you’re going to have to call someone to fix it and definitely swear a lot because the world is conspiring against you.

Like it did last week when you had to get someone to jump start your car. Twice. In the same day.

You can swear all you want, but you don’t have to call someone to fix the furnace pump. This is something you can do. Fixing or installing a condensate pump is pretty easy. In fact I had my pump delivered by the next day and installed in less than an hour.

If you’re reading this you have questions. I know this because I had questions, so I’m going to do what I can to answer them for you.

First of allllll …

What’s a condensate pump?

It’s a little water pump that sits right beside your furnace or central air conditioning system They’re about 5 x 7 x 11 inches with a small reservoir that holds around 1/2 gallon of water. Once the water hits a certain level, the float on it lifts (like a toilet float) and it activates the motor to start pumping out the water.

It does this over and over again throughout its lifetime. Sometimes once a day, sometimes many, many times a day. It’s called a condensate pump because it’s literally pumping out condensation (condensate) collected by your furnace.

What is the purpose of it?

To get rid of water. The condensate pump’s sole purpose in life is to take condensate water produced by your furnace, and pump it into a drain. The drain line from your furnace goes into the condensate pump, and then the pump pushes the water somewhere else.

Newer homes usually have a drain in the basement near the furnace, so you don’t need a condensate pump. The drain line can just drop right into the basement drain and gravity will do the rest.

However, if you have an older house you might not have a floor drain. The pump is needed to reroute the water to another drain in the house; often one or two floors above.

Some people refer to it as a drain pump but that’s not accurate. A “drain pump” is for pumping away grey water from sinks and tubs. (not sewer/toilet water) If you need to, by the way, I also have a post on how to install a toilet, which is much easier than you probably think.

Furnace or A/C leaking water underneath it?

If you see water under your furnace or A/C chances are your condensate pump isn’t working. It’s either clogged or the motor has died a dramatic death. If it’s clogged you can fix it, if the motor has died, it’s time to replace it.

How to check if a condensate pump is working

Before you buy a new pump you can run through a few tests to see if you can get it working again by checking for clogs, guck and goo. Those are the main reasons a pump won’t work. They’re also the main reasons your arteries won’t work.

  1. Silly I know, but always make sure that you have power and that you aren’t just dealing with a blown fuse, tripped breaker or a plug that’s come loose. If that doesn’t fix it go to step 2.
  1. Pour some water into the pump to see if it kicks in. If the pump turns on that means your motor is working and you might just have a clog.  The clog will either be in the discharge tube or the check valve.
  1. It’s easier to unclog a check valve so start with that. The check valve is what the discharge tube is attached to. It will just unscrew from the unit. (photo below) You’ll see if it’s gucky in there.
  2. If clogged, use a bottle brush and water to clean it. You can also blow it with compressed air. If you can’t clean out the stuck check valve but the motor is still working, you can replace your check valve instead of replacing the whole unit. Check with the manufacturer of your pump for your part number.

If none of this fixes the problem, go to step 4.

  1. Check to see if the discharge tube itself is clogged. Go to wherever the tube is supposed to drain (probably upstairs) and pour some water down it. If it makes it all the way out the other end, you know the tube isn’t clogged.
  2. If it is clogged you can unclog it using pressurized air or a shop vac. If the tube looks like a total disaster you can replace the vinyl tubing with the same size as is there now. It’s likely to be 3/8″ clear vinyl tubing. If the tube is clogged you can use a wet/dry vac, pressurized air or even pouring hot water down the tube.
  1. If none of this works it’s time to replace the pump.


Yes. If your condensate pump fails, you have to replace it. Otherwise your basement will be full of water in no time. If your furnace is in your attic that’s even more dangerous with the potential for your ceiling below caving in.

For a quick fix for a broken pump you can remove the pump and put a bucket under the drain line on the furnace. When the bucket is about half full, empty it then put it back.


  • Replacement pump that’s the same size as the one you have now.* (check the horse power and size of the reservoir)
  • Screwdriver
  • Scissors
  • Water

* Little Giant really does seem to have this market cornered so that’s what I bought for my furnace.


  1. Turn the power OFF. Either to your furnace or the entire house. Double check with a tester.
  1. Remove any water from the old pump with a turkey baster or syringe it.
  1. Remove the clear vinyl discharge tube from the pump.
  2. Disconnect the drain line(s) by carefully pulling the pump away from the furnace and tubes. (If your pump is servicing your furnace and A/C there will be 2 drain lines) Dump out the remaining water from the reservoir.

  1. Remove any clamps holding the condensate pump cord into place on the furnace.
  2. Remove the furnace cover and find the its electrical box.
  3. Remove the face from the electrical box and gently pull the wires out so you can access them.
  1. Take a PHOTO of how the wires are now so you can reference it later.
  1. Remove the marettes (the twist on caps over wire connections) and untwist the blue, brown and green wires. The green wire is the ground wire and will be attached to a screw at the back of the furnace’s electrical box.
  2. Once the wires are free you can pull the whole cord from the back of the electrical box and out the side of the furnace.
  1. Get your new pump and CUT the plug off of it. Scary. I know.
  2. Strip apx. 5″ of the sheathing from the new pump’s cord to reveal the 3 wires underneath. Be very careful not to nick the wires underneath when you remove the sheath.
  3. Strip apx. 1″ off of each of the wires (the blue, brown and green) and twist each one tightly.
  4. Bring the cord through the side of the furnace and in through the back of the electrical box.

  1. Referring to your photo, twist the wires back together in the same manner they came off.
  2. Screw on the marettes.
  3. Push the wires back into the electrical box.
  1. Replace the covers on the electrical box and the furnace. Clamp the cord to the furnace again to keep things tidy.
  2. Remove the tab from the new pump.
  3. Turn the power back on.
  1. Test your pump by pouring water into it.

Maintaining your pump

Keep it clean. The pump has plugs for the top to keep anything from falling into the pump reservoir. Use them. If something falls in the reservoir (like dust, debris, a piece of LEGO) it can get pumped into the discharge tube or check valve and clog it.

The main reason for clogging though is algae buildup. It gets in the reservoir and grows and grows and grows. That’s easy to prevent by dropping algae preventing tablets into the reservoir. Pan Tablets No. AC-912  will stop algae from growing and clogging any parts.


How long does a condensate pump last?

Maybe 1, maybe 15 years. Like any piece of small equipment with moving parts the more you take care of it the less likely it is to break down. Taking care of a condensate pump means keeping the inside of the casing, the tubing and check valve clean.

Is condensate water drinkable?

I wouldn’t but technically it is potable water that you could use in an emergency.

Can you use the water for anything?

A good use for any condensate water is for watering plants. I do it myself.

My seed starting setup is in my basement, but I don’t have a water source down there for watering. So using the condensate from my furnace is a perfect solution.

How long does it take to replace?

It depends on whether it’s hardwired or plugged in. Plugging in a new pump will take you all of about 4 seconds.

Replacing a hardwired pump, which involves wiring it to the inside of the furnace, will still only take around 45 minutes.

How much does it cost to replace a condensate pump?

If you DIY it, only the cost of the pump. My Little Giant replacement pump cost $59.

If you call an HVAC company, it will cost around $200.

What’s the safety switch?

Some pumps come with a safety switch built into it. When the pump is clogged and about to overflow, the safety switch will be triggered to sound an alarm or shut the furnace or air conditioner off completely.

If you have a pump without a safety switch, you can buy and install one on your unit.

Which type should you buy?

Just make sure you get the same size in terms of amps, voltage, and horsepower as the one you have now. Or check your furnace manual for their recommendation.

With that job done you can now have a seat, put your feet up and wait for the next thing to break.

Furnace Condensate Pump Installation & Repair


  1. Amrita says:

    I was looking at that thing the other day and was wondering what it was! I have never noticed it on any furnace before. Something to add to my to do list. Thanks!

  2. Lynn says:

    We don’t have that pump, very good read though.

  3. Randy P says:

    As an added benefit, most of the charger/jumpers out there have at least 1 USB port for charging cell phones, powering a laptop etc.

  4. Olivia’s grandma says:

    Honestly, I don’t know why I read this entire post because I will never, ever change/clean or replace the condensate pump on my furnace! But it was an informative read – I learned something I never knew: furnaces have condensate pumps!

    But Karen, I must tell you that Turkey blasters were renamed nearly 14 years ago by my then 3 year old granddaughter- they are now referred to as “sucker uppers.”


    • TucsonPatty says:

      That is a much better name!! I always love the words young children come up with when they don’t know the actual word. My daughter’s word for linoleum was “paper tile”. I loved it.

  5. Kathryn says:

    So glad you are back to share your knowledge. I knew I missed you, now I know why. LOL

  6. Petra says:

    Awesome practicum! Even though we don’t have a furnace or such a pump, We have a mini boiler connected to in floor heat connected alternately to hydro or solar. All very lovely but complex and if I lose my fixit guy I might be in a world of hurt.
    But I did buy myself a jump start gadget and have tasked Honey-do to draw up a schematic of the Lovely System in case he’s not actually one of the Immortals.

  7. Morgen says:

    How timely! My condensate pump barfed water all over our basement floor. For whatever reason, we do have a drain in the floor but it was still a mess. The condensate pump was clearly the culprit — full to the brim with water.

    In a moment of desperation, I whacked the top of the pump with my fist, “Fonz Style” and the pump kicked right on!

    I’m almost certain this is a temporary fix. Glad to know how to do it myself if it needs replacing soon and how easy it is to do. That way, if a repair guy shakes his head and says it will take half a day and cost $1000, I will know to call someone else.


    • Karen says:

      That’s half the benefit of KNOWING how to fix something. Even if you don’t do it yourself, you know exactly what’s involved, how long it should take and how much the part should cost. Then you know whether you’re being charged a reasonable amount by a professional. ~ karen!

  8. Randy P says:

    Great posting – my 85yr old Chicago Bungalow has hot water radiators, but I am WELL acquainted with the need to fix it myself for Oh-So-Many things over the 40yrs I’ve lived here. lol

    Oh – regarding jump starting? I picked up one of these dandy gizmos – there are a multitude of choices – to be able to self-rescue myself or easily help others. You might give them a look-see?

  9. Nancy says:

    I didn’t know what exactly that was. We bought a house with orange 1977 carpet in the basement. Yes, in the furnace area also. It was all wet but the pipe from the furnace wasn’t aimed correctly. I kinda shoved it over and zip tied it down for a better angle to drain correctly. My husband was happy. I better check it out better! Thanks.

  10. Cathy says:

    The only downside to a safety switch is having your furnace kick off in winter if you happen to be gone. Our furnace failed while we were in Fla back in the 60s and our pipes burst. I’m not claiming the pump failed as our furnace didn’t have one, but the result was devastating nonetheless.

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