If possible, check yourself.

If you know the basics of electronics, check the systerm yourself to determine what is the problem. when thermostat calls for heating, the control unit (the board) should sent high output to open the gas valve. If the control unit does not send high signal, the board is malfunctioning. Otherwise, something may be wrong with gas valve. Other than that, there are many other possibilities, such as bad thermal couple, bad pressure sensor (on exhaust duct) or exhaust duct clogged, etc.

I had the same problem as yours a few years ago: the furnace sometimes worked, and sometimes didn't. I stayed in front the furnace and watched how it started, and found sometimes the fire started but then went off right away. I measured the signal, and determined the gas valve was bad. I did not know how to changed gas valve, therefore called professional. He confirmed the problem, but I still paid $385 ($220 for parts,over changed). The control board can be found online (ebay?, forgot) for $120-150, and it is easy to change. by the way, my fornace was 14 yrs old when there was the problem.

Do it yourself. Do more, you know more.