Does the induced fraft fan come on at all? If the induced draft fan does not go on. Open blower compartment and jumper between r and w. There will be a door switch so you have to have someone hold that in for you while you jumper. If furnace comes on and heats bad tstat. Check this next Im right to get back to you quick now. Rus
Do you have a volt meter. If you do when the induced draft fan starts go across the contacts on the air switch to see if you get voltage. Also the tstat does bring on the induced draft fan correct. If the switch is made. Let the unit run and check voltage across limit switch that is located above burners. If one of them is open you will have 24 volts across them. Get back with me I am right here
There is only so far you can go without test equipment. You need to call a service. tech. You have more than one problem with this unit.