The condensate drain for my system is stopped up. How do I fix this?

A stopped up condensate drain can be a very common problem; and the symptoms of a stopped up drain do not always appear as such. First lets go over some common symptoms of this issue.

  • The air conditioning system is running, but intermittently. The system is not meeting the requested temp before shutting off abruptly. 
  • The air conditioning system is not running at all. Changing settings on the thermostat causes no response.
  • If thermostat is a digital screen type, thermostat may be blank. As if thermostat is getting no power. 
  • If air handler is located in attic, the secondary drain pan under air handler may be filled with water. The secondary pan is installed incase of a stopped up drain to catch the excess water, and prevent damage to your ceiling.
  • The secondary drain outlet of your air handler may have a float switch installed. Removing the cap of the float switch will reveal the secondary drain pipe and float switch are filled with water.
  • Any water damage to your ceiling under an attic air handler, or water leaking directly from any air handler in your home is potentially drain related.


Any of the above listed symptoms can be caused by a blocked drain line. Anytime water can't drain from your air handler, the water has to go somewhere. This often causes damage to your home or trips an installed float switch which shuts down the equipment. Let's assume that the problem has been identified as a blocked drain line, and go over some effective ways to fix the problem.

  • One easy way a homeowner can clear the condensate drain is to vacuum it with a shop vacuum from the outside of the home.  The condensate line can be vacuumed by placing the vacuum hose on the discharge of the condensate line.  An empty shop vacuum should be used for vacuuming the drain line.  This way after vacuuming, the vacuum can be inspected for the debris that was removed.  The vacuum hose should be left on the line for approximately two minutes.  After the time has passed, the homeowner will remove the hose from the line.  If the obstruction was sucked out, the drain should start draining on its own allowing all the water that was blocked in the drain pan of the air handler to flow out. 
  •  If the vacuuming technique doesn’t remove the obstruction, another way to clear the drain is by back flushing the drain with a water hose from the outside of the home.  The homeowner must take care when back flushing the drain to not flush to much water into the air handler causing it to overflow.  A few one to three second flushes applied to the discharge of the drain is usually enough to break the blockage loose.  A large flow of water, most of the time colder than the tap water, will signify the unstopping of the drain.  Once the blockage is dislodged, the debris should flow back out the drain with the water that was flushed in.


Try either of these methods to clear the drain. 

Also see the FAQ about Tripped Float Switches for more useful info.

Last update:
2016-06-12 18:11
Jacob Creamer
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