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Heat controller furnace will not lite and seems to have no power ( it does )

Furnace was working 2 weeks ago just fine. Now when the thermostat calls for heat nothing happens. It does have power to it but the only thing I can get to work is the blower. I bypassed the safety switch and tried a new thermostat. please help1

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Pilot generator may be bad if you have propane heat.In some cases that can indicate a low voltage short ,or could have a bad transformer on unit

Posted on Oct 03, 2008


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Furnace doesn't come on, no matter where thermostat is set

This sounds like the relay switch on the control board may be bad. I just replaced a control board last week on a Carrier unit doing the same thing. The relays are built into the control boards. To fix this you must call a luxaire dealer and they can be found at I will ask though, if you put the tstat into fan on instead of auto, does it come on? If it does, it could be a tstat issue. How you find this out is to remove the thermostat and expose the terminals. Take a small "jumper" wire and touch either one of the r terminals to the w terminal and hold it there. If the unit fires up with no problems, then it's the stat and not the board. Try jumping first and if it still won't come on, you know it's the control board. Good luck to both of you!

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Code 12 I believe is power up after power off and a call for heat from the the thermostat. If you have a weak door switch that may be vibrating and going on and off it would cause this as would any thing that causes the power to drop low or out then reapply its self. try holding the door switch in while watching the board and after 2 or 3 minutes the furnace should go on to lite and the blower cycle off. If it stays in this mode try turning the thermostat off (heat - OFF -cool) and then push in the door switch nothing should happen except the lite on the board come on and stay on. If it does this than have someone turn the thermostat to heat and see if it starts or put the door on and set the heat and see if *** goes through the normal cycle of heating. If however it goes right back into the blower mode and shows the 12 code your problem is still with you. So next remove the wire on the "W" terminal on the board. Retry power to the door switch and now nothing should be on except the red lite. If it tries to start the 12 code and blower up again Im pretty sure you have a bad ignition/blower control board.

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1 Answer

Gas furnace stopped; Thermostat to OFF;then ON after 5hrs-worked?

You have a carrier or bryant AC Coil model number and the sn says 1995 and its 5 tons and if you actually have a heat pump with the gas furnace you have what we call in the business a dual fule heatpump setup. There are a number of items that could be causing your problem. I would recomend that you first look for the relay box discribed below and if you have that put the wires at your furnace (R &W) together with nothing else on them. If it lites then the problem could be anywhere, thermostat, wiring, the control box which has about 4 to 6 relays. If it dosn't lite the furnace is where your problem is or at least one of your problems is and start there. remove anyother wires on R&W before reapplying power. Also if you have the control box below it will have its own 24v control transformer but your going around that with the test I mentiond here. Oh yes and if it hasnt been modified you'll have to keep the solid door on it to apply power to the furnace.

There are a multitude of items it could be but I believe your age furnace has an auxiliary sensor - relay assembly it is a box about 18 inches long X 6 inches square. has about 10 terminals on it. And it will look like a birds nest with all the wires going and comming out. Id have to suggest you call someone and here's what Id do if I were you. If they say they aren't sure but think its in the relay assembly for the dual fuel control ask them to call carrier or Bryant and request they talk to a service trained expert there or recomend someone. You can do this instead of paying for 2 people. Just ask them if they know about Bryant or Carrier Heatpump dual fuel setup before you tell them to come out.

The newer dual fuel thermostats around $300 - $400 plus an out door sensor about $30 will get you fixed for parts. NO more relay box needed just the out door sensor and the compatable thermostat. if this is where the problem leads. The thermostat cost will depend on if you want the program feature. If someone is home all day Id suggest you probably don't need this feature.

This should get you headed in the right direction. If it helps you please grasde me accordingly, and GOOD LUCK!

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