Furnace RUNS by itself, without interaction from wall thermostat


Old 09-18-09, 04:00 PM
Thread Starter
Join Date: Sep 2009
Location: Santa Ana, CA
Posts: 1
Received 0 Votes on 0 Posts
Furnace RUNS by itself, without interaction from wall thermostat

My “Day & Night” gas furnace, model 80cu12B,
series 152, “runs” by itself, without interaction from the wall thermostat. I tested the thermostat, and its OK. The furnace is the problem.
Any ideas?
Sponsored Links
Old 09-18-09, 04:29 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 35 Votes on 27 Posts
I have lots of ideas on numerous subjects. Why don't you tell us what you mean by "runs by itself" and also describe how you "tested" the thermostat. If you mean it is firing anytime the power is applied it may be in the thermostat wiring.
Old 09-18-09, 05:53 PM
Banned. Rule And/Or Policy Violation
Join Date: May 2007
Location: Wisconsin
Posts: 8,629
Received 0 Votes on 0 Posts
We need to know if the fan just runs?, or the heat along with it?

If it is heating without the stat, and you are sure the stat is disconnected (you can remove R wire on furnace terminal board - that wire feeds 24 volts ac current to the stat - to find out, or turn off furnace and ohm test R to W terminals and it should be dead. If continuity, this means thermsotat is still energized or thermostat wires are shorted), then you must be getting power through the W terminal connection anyway.

And if just the fan runs, since you are in CA?, maybe it is hot in the house and your fan switch setting is not right. Or you have a short somewhere between R(24 volt supply to stat) and G(to fan, from stat) terminals or wires.
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: