Problem: Draft inducer will not start, ignitor will not glow or gas valve will not open.
FYI: *You would be surprised how many people go without heat or cooling for hours/days and all the problem they have is the switch on the side of the furnace is not turned on or the blower door is loose after they change a filter! One customer blamed his cat for turning it off! LOL! I try to go over this with my customers before I make a service call so I do not waste their money.
Solution: Any combination of the above problem or problems could be caused by a bad furnace control board or bad draft inducer. I always troubleshoot and test the least expensive parts first, such as the thermostat, pressure switch, limit switch and rollout switches to make sure they are all closed and operating correctly before I go to the control board. First, and most important things to remember is turn your electrical power off to the furnace. We have a real good Youtube video below that shows the 8 top problems when a furnace draft inducer will not start. This excellent video was made by acservicetech. Thanks to acservicetech for making this great video!
1. The first thing that is supposed to start when a furnace starts up is the draft inducer. If the draft inducer does not start then you probably either have a thermostat , thermostat wiring problem, electrical problem, control board problem or a bad draft inducer.
2. Tape the blower door safety switch shut (if equipped) and set your thermostat so it is calling for heat. Us a volt meter set to “Volts AC” and test between terminals W (usually white wire) and C (Com) and see if you are getting 24 to 28 volts between these two terminals. If you are getting 24 to 28 volts between the W and C terminals then your thermostat and thermostat wiring are in good shape and doing what they are supposed to be doing. If you aren’t getting any voltage then you might have a bad thermostat, bad thermostat wiring, not getting 110 volts to the furnace (make sure switch on furnace is flipped on and blower door safety switch is pushed in) or a blown fuse on the control board. We have a picture of a fuse on the control board below. Most of the time you can get these fuses at a local hardware store. You would be surprised how many people go without heat or cooling for hours and days and all the problem they have is the switch on the side of the furnace is not turned on or the blower door is loose after they change a filter! I try to go over this with my customers before I make a service call. If the fuse on the control board is blown this usually means that you have a short in the low voltage circuit of the furnace. Most of the time I find that the animals have chewed through the thermostat wires and shorted them out or the thermostat wires over time have been pinched around the body of the furnace or air handler which has caused them to short out. You will probably need to replace your thermostat wire if you find it has shorted the fuse out. If the fuse does not fix the problem with the low voltage then you may have burnt out the transformer. We sell some transformers on the following page: Please click here if you are interested in seeing the transformers we sell. You should have a constant 24 to 28 volts AC between the R (red) and C (com) terminals on the control board no matter how the thermostat is set. This is the power coming right off the low voltage transformer. If you do not have 24 to 28 volts between R and C then you probably need a new transformer.
3. Most control boards are located in the blower compartment. Many control boards have a fuse located on them to protect the board from getting burned up if you have a short to ground. The fuse is usually a 3 to 5 amp fuse similar to the fuses that you might find in a car’s fuse box. Please see picture below of the furnace control board: If you find that the control board or draft inducer is at fault we sell many different types of control boards and draft inducers. Please send us your furnace’s model number and we will be glad to look it up and see which control board or draft inducer your furnace uses. Our email address is: firstname.lastname@example.org
If your fuse is blown you will want to check and see if any of the low voltage thermostat wires are touching the metal frame of the furnace or grounding out. Most of the time I see fuses that are blown from animals chewing through the thermostat wires and from the wires grounding out to the body of the furnace where the wires enter or exit the furnace. The vibration of the furnace over time sometimes wears through the wires insulation and causes a short to ground. I would try a new fuse first, then if the fuse blows again you are going to need to find out where the wires are shorting out. This can be quiet time consuming. If you get tired of burning up fuses we have a tool called the LiL Popper that has a button you can push in when the fuse blows instead of having to throw away fuses. We sell the Lil Popper on the following page: Please click here if you are interested in seeing the Lil Popper tool that we sell.
If your fuse is OK, tape your door safety switch shut so you can view the status LED light on the control board with the furnace power on. Please remember to turn the power back off before touching anything inside the furnace. I do not want to hear of anyone getting hurt or shocked! Turn your thermostat up so it is calling for heat. Let the furnace cycle and see if the Status LED flashes a code. The directions for reading the code are usually located on the furnace door. The code will usually tell you what is wrong with the furnace. Technology is amazing! Best of luck on repairing your furnace. Please remember to turn that power back off before touching anything.