Return to the Heating & Air Conditioning Forum | Post a Follow-Up

Comfortmaker Furnace won't start, but A/C does. Please Help!

Posted by proenpro (My Page) on
Sat, Oct 29, 11 at 22:12


I have two newer (~ two y/o) Comfortmaker furnaces, one for my first floor and the other for my second. The one for the first is working fine, but second floor heat does not go on. I began troubleshooting the faulty second floor furnace by replacing the thermostat, hoping that that would resolve the problem, but that did not work. The non-functioning system's diagnostic code (three long flashes) on the control board indicates "pressure switch is open when should be closed." While on the good system I've got the "heartbeat, or normal operation" - steady quick flashing.

When I power off/on breaker for the bad system the control board has a heartbeat for about a minute, then switches to the three long flashes (when thermostat set to heat). I tested the A/C on the faulty system and it works fine, with control board maintaining a steady, consistent heartbeat.

Additionally, I've powered off both systems at breaker, disconnected wiring from the pressure switches, checked them out with multimeter and both read the same (1), which leads me to believe that the pressure switch on faulty system is good.

I'm confused. Any advice or assistance would be greatly appreciated.

Many thanks in advance,


Follow-Up Postings:

RE: Comfortmaker Furnace won't start, but A/C does. Please Help!

How old is your furnace ? If it has a draft inducer blower motor, it must be working properly and up to speed. This closes the pressure switch and starts the ignition of the furnace. To make sure there is no problem with the exhaust or inlet, check them out. Very likely change the draft blower and it will work.

RE: Comfortmaker Furnace won't start, but A/C does. Please Help!

icemate is off base, sounds like a clogged hose.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Heating & Air Conditioning Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here