Save your life, not your money. Call an expert. Had almost the same thing happen here this Fall. It was the heat exchanger and it was leaking CO into the system. The system shut down and I started to replace the obviously failing part. That would have been a very bad mistake! The system would have started working again, but pumping CO into the environment. Probably wouldn't have killed us, but?
Fix your lights, fix your TV, fix your stero, fix your computer, plant petunias, dig your own drainage, fix your own AC, fix your roof - CALL A PRO FOR THE HEATING SYSTEM!