In the furnace plenum there is a flapper ("sail" switch) that closes a switch when the furnace calls for heat. The blower MUST run in order to move the flapper. A fire hazard would exist if the furnace was allowed to fire without the blower running.
I attached the Suburban manual.
Things that need to work to fire the propane (in order):
1) The thermostat needs to "call for heat" - it does
2) The furnace control board must route power to the blower - The fan MUST start to fire the propane - unknown - is the fan running?
3) Once the fan is turning, the "sail" switch must close to route power to the propane solenoid valve to let propane into the fire chamber - do you smell gas outside? Is there voltage at the solenoid?
4) The air fuel mixture must be right for ignition. Mud daubers, dust, and dirt can clog the orifice and air inlets on the burner tube to yield an over -rich mixture, too rich to light.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW