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HVAC Guru
HVAC Guru, HVAC TECH
Category: HVAC
Satisfied Customers: 5439
Experience:  15yrs in the HVAC industry with certificates and degrees.
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My furnace wont start when the thermostat calls for heat.

Resolved Question:

My furnace won't start when the thermostat calls for heat. The draft inducer motor
never stops. I can get the ignitor to start by shutting off the power for a few seconds.
When I do that(power off then back on) the ignitor glows,the gas comes on and the
furnace runs normally until the next time heat is called for.
Submitted: 1 year ago.
Category: HVAC
Expert:  HVAC Guru replied 1 year ago.
Have you watched it when it calls for heat the next time to see if it tries to light again? Does the ingitor come on the second time?
Customer: replied 1 year ago.

I have not tried that If you want me to try that it will be a few hours


because it is running now so I will have to wait until it stops at 72 degees


and the find somebody to turn the thermostat up while I watch in the basement.

Expert:  HVAC Guru replied 1 year ago.
Yes do that and get back to me I will be in and out as well, but will get back to you.
Customer: replied 1 year ago.

OK STAND BY

Expert:  HVAC Guru replied 1 year ago.
Yep no problem
Customer: replied 1 year ago.

Your test won't work because the themostat has already called for heat


(and failed) before I crank up the temp to look for a start.My thermostat is set at 72. The temp was down to 70 when we tried your test by turning it


up to 75. t did not start until I turned the power off then on again. I think


what I would have to do is set the stat down to a low number where the


room temp is much higher and then try your test. If that is correct let me know and I will do it that way. STANDING BY

Expert:  HVAC Guru replied 1 year ago.
You may have an issue with the thermostat itself. Make sure the batteries are replaced on the thermostat. Also you can take the thermostat off the wall so you can see wires. If it is not starting, twist RH and the W wires together when it does not start or jump the wires at the terminals with a paperclip. See if it comes on. If the furnace starts up just fine I would say you have a bad thermostat.
Customer: replied 1 year ago.

With the room temp over 73 we turned the stat down to 55 to make sure it was off. With me watching the furnace and my assistant turning the temp


of the thermostat up to 85 there was no start or atempted start. I did my usual by turning off the power to get a start which worked as usual. The


thermostat test above I don't think I will be able to do until tomorrow. Let me


know if the above test requires the thermostat test.


 

Expert:  HVAC Guru replied 1 year ago.
Yes I believe you have a thermostat problem. You have to manually jump the wires at the thermostat or at the furnace board. If it starts up you have a thermostat issue.
Customer: replied 1 year ago.

I have changed the batteries in the stat and will try jumping the terminals


tomorrow. Will report to you then.

Expert:  HVAC Guru replied 1 year ago.
Ok great!
Customer: replied 1 year ago.

OK will do the jump test tomorrow. Meanwhile think about how the water


drain line to the sewer would effect our problem if clogged.

Expert:  HVAC Guru replied 1 year ago.
It should not unless you have a condensate sensor that has been activated by the back up in water. Normally it would never come on though
Expert:  HVAC Guru replied 1 year ago.
One of the other good techs on here brought up a great point. If the inducer motor is never shutting off then it will never be able to call for heat again. If that is the case then the relay on the control board is bad and stuck closed for the inducer motor.
Customer: replied 1 year ago.

My thermostat has terminals RC(red wire) and W (white wire) I assume

you wanted me to jump the red and white wire. I did jump the red and white

which had no effect . While holding the jumper in place I tried my power

off and back on trick and got a re-start. As soon as it started I pulled the

jumper and the furnace shut down.Meanwhile the inducer motor keeps

running.

Is the inducer motor relay soldered to the board or is it a plug

in relay?

Expert:  HVAC Guru replied 1 year ago.
The inducer relay would be part of the board. If that is happening you will need to replace the board. That for sure is the issue here.
Customer: replied 1 year ago.

You are 100% sure it is the board ?

Expert:  HVAC Guru replied 1 year ago.
Yes it is the board.
Customer: replied 1 year ago.

OK I am on my way to pick up the $165.00 board. Will report back to you


after it is installed

Expert:  HVAC Guru replied 1 year ago.
ok no problem
Customer: replied 1 year ago.

The board is replaced and everything seems to be working, I will confirm


after a few more cycles

Expert:  HVAC Guru replied 1 year ago.
OK GREAT! Please rate my assistance..thanks!
HVAC Guru, HVAC TECH
Category: HVAC
Satisfied Customers: 5439
Experience: 15yrs in the HVAC industry with certificates and degrees.
HVAC Guru and 2 other HVAC Specialists are ready to help you

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