My furnace won't come on. This happened once last year and was told that there may be a shortage in the circuit board, and it'll have to be replaced if it happens again. They told me a sure sign would be if I had a problem with the ac coming on in the summer. Well, no problem with the ac this year and furnace was working fine up until now. What do you recommend I do for tonight and how much should I expect to spend for a technician to replace a Carrier furnace circuit board?