did you find you problem?
I’m not sure of your system but if you just have a simple gas heater, not a heat pump or eclectic heater in the AC, this will give you a good start.
Easy checks: Do you have good 12v dc(battery disconnect?), change out fuse, be sure there are no loose wires on thermostat.
Multimeter: turn thermostat to call for heat check to see if you’re getting 12v dc out of thermostat, check fuse just to be sure
Well that’s all the easy stuff I can think of. If none of those things got you going, next is to get to the heater. Careful of the sheet metal heater housing, they are notorious for razor sharp edges. Inspect for any mouse activity, chewed wires. Check for any loose wires. This may sound bad but give the board a few taps and give the blower a few whacks while calling for heat.
Somewhere in here is your problem or at least a good start. It’s a puzzle, one piece at a time and you’ll find what’s missing
Multimeter: check for 12v at board from fuse, find signal wire from thermostat and check for 12v when calling for heat, check to see if getting 12v to blower while calling for heat.