HVAC Questions? Ask an HVAC Expert for Answers ASAP
Yes I think so as I can smell combustion gas.
to this question I can't answer as I am not at my furnace - I am at work. Will I have to open the top cabinet of the gas pack to see this or can it be seen with the front panel off?
It can be seen through the front panel, but I would prefer for you to remove the front panel off because we may need to perform troubleshooting test. When troubleshooting a Furnace, the first step is to know the operation process. Once you learn the operation process, then you watch the furnace go through this process and wherever it fails, that is your problem. Then you have to find out why it is failing at this particular point. Here is the Operation process of a gas furnace:
1)Thermostat is set to call for heat
2)Inducer Fan Motor starts (prepurging system of flue gases)
3)pressure switch closes
4)Igniter attempts ignition (spark or glow coil)
5)gas valve opens to light burners
6)Flame Sensor proves flame is present
7)control board allows gas valve to remain open since flame is present
8)Heat Exchanger heats up & blower motor starts
I will need you to observe the Ignition process of your furnace and compare it to this process and let me know where your furnace fails.
I will try to observe the ignition process later today. Just to get a little more insight on this problem I have another couple questions.
What creates the air pressure that trips the pressure switch? Could there be insufficient air pressure or a leak or a bad switch?
I live in NC and often this problem has arisen in October where we get a few cold nights middle of the month and the furnace comes on at night and works normally for many days. Then we get warm weather again for a couple days and switch back to using A/C for a day or two. It is then the reversion back to heat (yesterday) that we run into this problem...but after "fixing" this by "rebooting- power on/off" we don't have the problem again for rest of fall/winter. Puzzling...
Followed your advice. No change. Could it be inducer motor not drawing enough vacuum. Is it normal that the inducer fan shuts down after about 15-20 seconds after the heat is called for?
Remove the two wires attached to the pressure switch. Attach them together metal to mtetal and attempt ignition. See if the igniter attempts ignition while you are holding the two wires together metal to metal.
Also it is not normal for the inducer fan to shut off before the pressure switch is closed.
did that. no ignition.
Did the ignitor attempt to ignite (spark or glow coil)? If not, that is an indication that your igniter is bad and needs to be replaced. But before you condemn it, use a voltmeter to see if the igniter is getting voltage at the point of ignition.
Had a tech come out this morning. He positively diagnosed as the "flame roll-out sensor". He replaced it and now have heat.
I apologize that we could not solve your issue. We are happy that your issue is resolved.
Thanks for the info.