I've been having intermittent issues with my approximately 15+ year
old furnace. The thermostat is calling for heat and the fan is on,
however the furnace won't light up. It works fine if you open the
furnace and switch to manual. I've checked the thermostat and it
works fine. I've read where these furnaces have a lot of different
problems, but I'm not sure what the issue is with this.