I have been having problems with my Criterion II ignighting. Here is a list of events that usually happens but not always.
Furnace gets signal from thermostat for heat and the small fan starts
the ignitor will start to glow then you can here the gas valve open and the chamber where the ignitor is will lite but not the other 4 chambers.
This is when the gas will shut off after a few seconds and the system will continue the cycle again until either it will light or go into lock out mode.
This is happening very random. Some days it works everytime without problems and other days it has issues all day long.
I was told by the Rheem service tech who was here installing my central air this summer that it was the flame sensor and it needed cleaned (free advice from him) I have done the cleaning thing and it didn't work so I replaced it and no luck there so it's not the problem.
It has been doing this for several years and I'm getting tired of it.