Gas furnace repairs aren’t that difficult for your standard 80% furnaces. How do you identifying an 80% furnace? First, the furnace has steel flue pipe above the furnace leading to your chimney. Second, the furnace has only one pressure switch.
The tag or name plate inside your furnace is where the model and serial number is at. It will also tell you what your furnace is, If it does not, you can take the model number, type it into the address bar on your browser, and you should be able to find a match. This will also give you more information about your furnace.
If you have a standard 80% furnace and the furnace will not turn on, what do you want to check? Most 80% furnaces have a little red light on the circuit control board (usually found in the bottom door in the blower compartment). Look and see if the light is on with the door panel in place (there should be a peep hole). If not, remove the bottom door and hold the door switch in. If the light is on, you have 24 volts from your transformer supplying your low voltage circuits. Another simple test is to put your fan selector switch from your thermostat to fan on. If the fan comes on, you have 24 volts feeding your circuit. If either of these tests don’t work, your transformer may be defective. Of course your thermostat may be defective as well.
How do you determining if your thermostat is good or not? Turn off your furnace switch on the side of the furnace. Next, remove your thermostat and take the little red wire off the R terminal of the thermostat, Do the same for the white wire or the W terminal. Now, twist the red and white wire together and turn the switch of the furnace back on. If the furnace fires up and works properly, your thermostat is defective.
Always remember to turn the power off to the furnace before this procedure is performed as well as keeping the power to the furnace off while replacing your thermostat. When installing your new thermostat and you have central air conditioning, make sure you keep the factory installed jumper wire that is on the RH and RC on the thermostat, put the red wire on either terminal. Also, always make sure your furnace filter is clean.