House heater redux

So I had the professional come in. He discovered that the filters were dirty and that the limit switch was off. He cleaned the filters and reset the limit switch, and it worked for a few hours or maybe even days (It got warm so it was hard to tell}. Now it is cold and now it is broken in the same way. I pulled out the filters reset the limit switch and it worked again for maybe half an hour. Given what I have told you so far, what is/are the likeliest cause of this problem.

Clean your flame sensor and see if that works. It’s easy as pie and free, and nearly impossible to mess up. If that doesn’t work THEN call someone.