I have a heil sp80 furnace. The furnace will not light in the gas chamber, I feel like there is no gas there to light. Thermostat calls for heat - combustion fan starts-igniter glows - then nothing other then it keeps trying on its schedule. I changed the smart valve thinking that was it, but it was not. I'm thinking control board, but I'm open to other sugestions. Any help is much appreciated, thanks