If it’s the first time you turn the heat on for the cooler weather and it doesn’t kick on, or sounds like it’s trying to but then gives up, you might have rust or some type of blockage in your vacuum line. I’m not an ac tech, so I can’t really help beyond this but I’m told this is a common occurrence. If your system looks different than this one and the equivalent parts aren’t obvious, I’d call a pro or find a more suitable you tube tutorial. I do know it’s a safety mechanism to keep the system from running if the gas isn’t lit, so don’t get clever and try to bypass it somehow. Good luck and I hope this video helps!