How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask HVAC Guru Your Own Question
HVAC Guru
HVAC Guru, HVAC TECH
Category: HVAC
Satisfied Customers: 13961
Experience:  15yrs in the HVAC industry with certificates and degrees.
21107370
Type Your HVAC Question Here...
HVAC Guru is online now
A new question is answered every 9 seconds

I think that I may have a bad furnace control board. Trouble

Customer Question

Hello I think that I may have a bad furnace control board.
Trouble shooting so far.
Two different thermostats with the same behavior.
Direct connection of the R&W&G wires make the furnace run continuously
The furnace starts up and runs fine for a minute or so and then shuts off. This happens with both a Nest thermostat as well as a Honeywell thermostat. Troubleshooting with a Nest engineer the power appears to "go off" at the one minute mark, this is where the furnace stops working.
Steps taken
Removed and cleaned heat sensor with 1200 grit emrory cloth and tested with ohm meter, sensor appears fine.
Thanks in advance Dave Couch
Submitted: 15 days ago.
Category: HVAC
Expert:  Rick replied 15 days ago.

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can continue our conversation.

If you jump R & G fan will run continuously. You need to just jump R & W. How does the furnace behave then?

Customer: replied 15 days ago.
not sure but I can try that. The furnace control board is a Lennox BCC3-2. Do you want me to try the above steps now?
Expert:  Rick replied 15 days ago.

If you want to do this now then yes.

Customer: replied 15 days ago.
ok hold on a moment and I will give it a shot.
Expert:  Rick replied 15 days ago.

Ok

Customer: replied 15 days ago.
Ok just jumpered the R&W wires and turned the furnace back on. It ran for 1-2 minutes and then shut off.
Expert:  Rick replied 15 days ago.

What are you getting for an LED flash sequence? What is the model number of the unit?

Customer: replied 15 days ago.
the model is a Lennox BCC3-2, not sure about LED flashing but will check.
Expert:  Rick replied 15 days ago.

That's the board I need the furnace model not the board

Customer: replied 15 days ago.
No LED's to flash.
Expert:  Rick replied 15 days ago.

model number? are the LED's lit?

Customer: replied 15 days ago.
Sorry mis-understood question, Lennox elite M/N G23Q2/3-75-2
Expert:  Rick replied 15 days ago.

Are the LED's lit? if not do you have the blower compartment door in place so the door panel switch is engaged?

Customer: replied 15 days ago.
no led's on unit, I buttoned up the unit before last test and also manually held the door panel switch on a different test.
Expert:  Rick replied 15 days ago.

There are 2 LED's on this control board.

Customer: replied 15 days ago.
Hmm then I guess neither are lit, will check again. thanks for your patience.
Expert:  Rick replied 15 days ago.

ok

Customer: replied 15 days ago.
I am starting to suspect that I have a bad door safety switch. Just held it in place for the past 5 or so minutes and the heater ran without shutting down. I may try putting everything back in place and jumpering the switch as a test.
Expert:  Rick replied 15 days ago.

That would explain a lot. That switch is not critical. Jumping it out is a good option.

Customer: replied 15 days ago.
I will let you know in a few minutes, running test now.
Expert:  Rick replied 15 days ago.

Ok

Customer: replied 15 days ago.
No joy, with jumper and door on it runs about 1-2 minutes. With bottom door off holding the switch closed it ran about 5 minutes. Weird.
Expert:  Rick replied 15 days ago.

So what are the LED's doing?

Customer: replied 15 days ago.
I cannot find any LED's on that BCC3-2 board or on the schematic that I have for it.
Expert:  Rick replied 15 days ago.

I'm logging off for the night. I'm going to open this up to my colleagues so one of them can help. Please don't respond (even to acknowledge this post)until you get a response from us. If you respond first it will only delay your answer.

Expert:  HVAC Guru replied 15 days ago.

Hello and thanks for using this service! If you are a JA Member I would like to personally thank you and welcome you back! I am HVAC Guru an extremely experienced tech on the site and I try to get to as many customers as I can. NOTE it takes time for me to type research and add links so please wait for me to respond back I can only do this so fast. Secondly, I do not know your skill level so please try and let me know if I am going beyond your knowledge or comfort zone thanks! I strive for a 5 star rating from everyone especially our JA members.

Is the blower running when it does heat?

Customer: replied 15 days ago.
Hi, here is where my trouble shooting is so far.
I noticed that when I manually depressed the lower door switch the flame/blower ran for as long as I cared to hold the lower door switch closed for.So then I put a jumper across the door switch leads to troubleshoot if the door switch was bad. Then I put the bottom door back in place and got the same result as before. The furnace would run for a minute or two and then shut down. Then I opened lower door and the furnace ran fine.I pulled the filter to see if it was plugged, it was fine I just replaced it a few weeks ago. I ran the same test as above and the only way I can keep the furnace running is to jumper the lower door switch and then remove the lower door. I kept the upper door in place.Does this point to a direction that I can only run with the lower door removed and the door switch jumpered?
thanks
Expert:  HVAC Guru replied 15 days ago.

Sounds like you may have an air intake issue. If it runs fine with the door off and switch jumpered then I would check the air intake pipe for a blockage.

All I ask is please use the Star Rating Link at the top of your page before leaving, that is the only way I am credited through the site, tips are appreciated.

Customer: replied 15 days ago.
There is no air intake pipe. There is the air return bot no outside makeup air pipe. Is that the pipe you are referring too or is it something different?
Expert:  HVAC Guru replied 13 days ago.

So it runs fine with the door off?

Customer: replied 13 days ago.
sorry I have been out of town for the weekend. The furnace, Lennox Elite Series from 1995 Model number G23Q2/3-75-2 has suddenly started doing weird things. It has been working fine with the AC all summer and when I started the heating unit on it up this year it developed the above symptoms. I can run it with the bottom door off and the safety switch jumpered. If I close it back up (safety switch either jumpered or not) it will run for a minute or two and then shut off. I am out of ideas on it and I am considering if it is safe to run with hole cut in the lower door and put a filter between that and the blower motor or not.
dc
Expert:  HVAC Guru replied 10 days ago.

That has to be an intake air issue. It is starving for air.

Related HVAC Questions