Our thermostat stopped working as there was no power on the Rc line. After a bit of investigation I discovered that the HVAC unit (Model number ARUF25B14AC) had water in the drip tray, which had caused the moisture sensor to switch things off.

I did a bit of research online and apparently this is usually due to the overflow pipe becoming clogged. This will make sense as we've not been running the unit due to cooler weather, but the attic where the HVAC is located is warm so it's a perfect environment for the pipe to become gunked up (damp and warm!).

The problem is that I'm having some trouble removing the overflow pipe to clean it.

Picture of overflow pipe connected to the HVAC

Picture of plastic overflow pipe connected to copper pipe

I can move the pipes up and down a few inches which causes the light grey plastic to move in and out a bit. I can't unscrew the pipe bolts as it feels like I'll break something.

Close up of the fastener where the overflow connects to the HVAC system

Do I need to loosen this fastener? If so what is this type of fastener, or the tool I need called?

Any tips appreciated. I'm close to calling a HVAC technician but I think I'm close to fixing the issue myself!

Update: I had a technician come around to take a look as I didn't want to start cutting things and causing more damage. They diagnosed the issue as being a tripped system which caused the unit outside to stop working problem, which resulted in condensation building up in the main unit inside. They reset and and repaired things and it's running fine now. I'll keep an eye on it though to make sure the overflow pipe doesn't start dripping again.

I'm a little skeptical about the tripping diagnosis as no one touched the thermostat in months as they insisted.

  • 2
    Can you find the other end of the pipe (or a cleanout port)? you might be able to clear it from the other end with a bit of pressure Commented Jun 6, 2023 at 15:08
  • 3
    Stick a shop vac on the end of it.
    – isherwood
    Commented Jun 6, 2023 at 15:23
  • I just followed the pipe all the way to the corner of the attic. It goes outside, but there's cladding covering from the outside of the house so I can't see where it ends
    – MrK
    Commented Jun 6, 2023 at 15:33
  • @MrK if you can see where it leaves the attic then go outside to where that is and just look around for some pipe sticking out. It's got to be somewhere. Commented Jun 7, 2023 at 14:23
  • 1
    The Red Plug may or may not be for adding a second pipe. The Gray Plastic Bit is likely part of the drip tray, or attached to it. You should be able to take out a few screws to open up the unit and look — tho you may not see much. Or, obvs, yewTube for a general idea.
    – Steve I
    Commented Jun 8, 2023 at 7:44

4 Answers 4


Those white PVC fittings are likely to be glued (and the piece that goes into your AC unit is likely threaded/screwed into place), so you're probably not going to be able to just easily disassemble the piping. I would guess that the red piece is a threaded insert that could be screwed out, but not sure that'll give you any good access to clean out the drain line. But in absence of being able to get into your AC unit and clean that drain line out from the inside out, you'll probably need to try and clean it out from the outside and hope it's not a long run of PVC pipe.

In absence of any other options, you may need to cut the white pipe in a good location and clean it out from both directions, then use a PVC union to connect the pieces back together to easily disassemble in the future, as if it has gunked up once, it's sure to gunk up again.

  • A "no hub" connector would do as well, if you'd rather not deal with cement fittings.
    – isherwood
    Commented Jun 6, 2023 at 15:33
  • I've added another photo showing the plastic piping connected to what I'm guessing is a copper pipe, which runs all the way to the outside of the house. I'm thinking I need to cut the smaller PVC pipe, clean it out and add a new section that allows for easy access in the future like you suggest
    – MrK
    Commented Jun 6, 2023 at 15:39
  • I've updated the question with what a technician found. It meant we never cut the pipe, but since that's what I originally asked advice for I'm marking this answer as accepted. Thanks for the advice!
    – MrK
    Commented Jun 9, 2023 at 15:52

Typically the way to clean these out is to use a shop vac at the far end and suck the gunk out. Since you don't know where that goes, you can't do that. But that's also a problem. You really need to know where that goes.

If you can't or don't want to use a shop vac, you can use a garden hose instead if you plumb in 2 valves and a garden hose fitting. You just have to make sure you don't allow water to get in to your air handler.

In the picture below, you can see 2 valves and a garden hose fitting. Normally, the valve to the garden hose fitting is closed, and the other one is open. This allows the AC to drain.

To flush the line, connect a garden hose and turn it on. Then close the valve on the AC side, and open the valve on the garden hose side. Let it run for a few seconds, then close the garden hose side and open the AC side.

enter image description here

  • Some of the big box hardware stores will let you rent a shop-vac if you want to use one just for this and not buy it outright. Alternatively, wet-dry vacs or rug-shampooers may work if they have a detachable hose as many of them do, and these can also be rented. If it's short enough, you could even use a plumbing snake, but all of these would require knowing where the end is. Commented Jun 7, 2023 at 17:09

If the original installer was a good one, it's likely that some of the PVC fittings glued, but not all — for exactly this reason.

In your photos some are obviously glued and others are... well, hard to tell from a photo. It may be worth getting out the big pliers and checking for any that are friction-fit. PVC does tend to stick, though I have found silicone spray works well as "one-time lube" for getting plastic parts loose without worrying about long-term damage.

Edit: Of course if they are all glued you will need a saw, as other answers already suggest. A good opportunity to add a proper cleanout, since your install scenario is so obviously one likely to need cleaning. My experience has been with installs that have a condensate pump that will need to be replaced, so friction-fit makes more sense.

  • 1
    Well you wouldn't want to saw the PVC. You'd want to get a ratcheting PVC cutter like this one Commented Jun 7, 2023 at 14:19
  • 2
    @DeanMacGregor - Why? To just cut out a section and do it properly a hacksaw and a deburr is fine. The only reason for those cutters is if you're using PEX and push-fit connectors, or cutting a LOT of pipe.
    – SiHa
    Commented Jun 7, 2023 at 14:36
  • @SiHa well I guess it depends if you just have a good hacksaw anyways or need to buy a tool regardless. My point, which I admittedly failed to articulate, is that if you're going to buy a tool to cut that pipe then buy the tool made for cutting pvc pipe rather than a hacksaw. Commented Jun 7, 2023 at 14:55
  • 2
    @DeanMacGregor Well, sure, I guess. I suppose I'm assuming that just about everybody will have a saw capable of cutting some PVC pipe, so there's no need to buy a tool for this one-time use. You said "You wouldn't want to saw that PVC", which is plain nonsense.
    – SiHa
    Commented Jun 7, 2023 at 14:59
  • @DeanMacGregor - Good point. Sawing PVC pipe is messy. Sawing PVC pipe full of water and guck is REALLY messy!
    – Steve I
    Commented Jun 8, 2023 at 7:47

Your AC should have a condensate trap. This prevents suction of air into the blower through the drain which in turn improves drainage.

Some condensate traps include cleanout ports so you can use brushes and compressed air to clean the pipe.

Saw out and remove the whole PVC section and install one.

Here is an example. enter image description here

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