You replaced the common parts and still no 120 V at the ignitor connector. I suspect the problem is the relay feeding the 120 V. If you can check the voltage to the input and output of the relay. It might be stuck in the open position. Try gently tapping it to see if you can get it to engage while the thermostat is calling for heat.

Thank you for the suggestion. in this furnace there is no individual relay in the circuit for the 120vac. The voltage to the ignitor is controlled by the White Rodgers Ignition Control module. i will however, recheck the voltage TO to the module.

Well I'm not much of a help telling you to tap a relay that doesn't exist. My fault for not reading your initial post more carefully and doing better research.

What is the model number of the White Rogers Ignition control module? There may be a trouble shooting video available to help figure this out.

It's a 50E47-70. I replaced it with a Universal 50E47-843. Another sympton that I didn't mention is that the ventor motor comes on immediately after I set the thermostat to heat but then goes off for 1 sec then back on again and stays on. I'm also not hearing the relay in the gas value come on that might indicate no voltage there either.

HU….it’s my understanding that the hot surface ignitor will not read voltage until that step in the sequence of opeations is reached, and prior steps have been satisfied. In this case…the thermostat has called for heat (or heat is jumped out), the inducer motor has started and the pressure switch has closed. You mentioned that you have recently replaced the pressure switch. You also mentioned that the draft motor starts for a second, stops and restarts. I have never witnessed this hapening before. Does your inducer motor have a limit switch built into its’ housing? My gut feeling is that there may be an issue with your inducer motor. Maybe some sort of blockage? If it does have a limit switch built in check to see it that is working? Can you confirm that the air pressure switch is proving? You won’t see voltage at the gas valve either or hear the click until that step in the sequence is reached and all other prior sequence of operatoins satisfied. If your ignitor never recieves voltage it won’t tell the board to send voltage to the gas valve. If I’m off here I aplogize. I’m still learning but wanted to share what I though may be the issue.

Good news! Problem solved. I was getting a reverse polarity code on the ignitor module. It turns out the the furnace was wired "backwards" for 30 years.....neutral and hot were reversed. Does anyone know why it would have worked all these years? It suddently stopped working this year. After a lot of troubleshooting, I realized what was wrong, switched the hot and neutral to the correct positions and...it works! What could of changed in the furnace or the house to have caused this problem? Thx!!!!

The furnace housing is usually not connected to the neutral connection so swapping the hot and neutral wires should not matter. The original 50E47 module failed after 30 years, but the Universal 50E47-843 does not work with swapped wiring. I can't think of a reason why it would not. You would have to study the schematic of the module for a possible reason.

Good work at troubleshooting the problem and coming up with a solution. Sorry I wasn't more of a help. I actually enjoy trying to solve problems like this.

Thx for your help. The only logical explanation is that the 50E47-70 failed for whatever reason but was not sensitive to reversed polarity of the line voltage. Once i repaced it with the 50E47-843 the original problem was likely solved but….this newer controller has the polarity sensitivity. Once i corrected the input line polarity (connecting hot to hot and neutral to neutral right where the line comes into the furnace) the furnace operated normally. Without the yellow flashing error code on the new -843 controller i never would have thought about polarity and never would have found it. Gotta love technology!