I have an American Standard Freedom 80 that is about 10 years old. At the end of winter last year it stopped heating the air but kept circulating it, pushing cold air through the vents. Now that it is starting to get cold again, I climbed up into the attic to check on it and found that the hot surface igniter was broken, the tip was broken off and it didn't get hot even though it had about 105 volts A/C.
I went to the hardware store today and picked up a universal hot surface igniter
from Home Depot to replace it, wired it up, and mounted it. When the furnace kicked on it glowed red hot so I thought my problem was solved. After a few more seconds the gas came on for about four seconds, but it didn't light. The furnace would cycle the HSI and gas a few more times before the blower turned off and the fan turned on. The control board's LED was blinking constantly before, but switched to just two blinks after the blower shut off and the fan started. I thought the igniter might not have been in the right place, but even after adjusting the HSI it still wouldn't light.
I'm not sure where to go from here, it seems like it should be working. I have a few ideas but I'm not really sure how likely they are:
1) The hot surface igniter is not getting hot enough.
It glowed red hot, but the picture on the box shows it getting white hot. I wonder if it is supposed to be getting 120 volts (110 is the lowest I recall reading online) instead of 105 volts I measured.
2) The hot surface igniter is not positioned correctly.
I picked the bracket that I thought was the closest, but I don't think it is in the same spot as the original. I don't really think this is the problem though because I moved the HSI around and even put it right in front of the gas diffuser (not the initial jet, just to be clear) but it still didn't light.
3) The gas jets are dirty and need to be cleaned.
This seems less likely because I felt them and they felt clean and smooth, but I wasn't able to see them because of the angle.