Our old house has a pilot light but it wasn't always lit. The thermostat would turn on a small valve to the small polit light and a spark ignitor would keep ticking away. Then that small flame would heat up the thermocouple and open the main valve for the main flame. One morning the thermocouple failed. It was a small box that plugged into the valve and then had a stiff wire coming out that the small polit like flame hit. I took the nuts off the bolt for the small box and found that it basically pressed a button that opened the valve so I was able to sit there holding the button down for a while until the house got back up to a decent temperature and then go buy a new thermocouple which for that old furnace was $79.
The blower fan motor sized up a couple times in the 13 yeras I was there, a little oil dripped in the shaft got it going until the third time I had to buy a new motor for $120.