Installed Bryant Plus 90 398AAZ furnace in 1991 as a backup to a heat pump so it was rarely used until 2006 when the heat pump died and it became the primary system. Furnace heats the 1st floor only. Since 2006 there have been 5 occasions (today being the 5th) when I wake up to a cold first floor - thermostat timer goes on at 6am, off at 10pm. On 2 of the previous occasions, I turned the thermostat off, waited a few minutes and turned it back on and there was heat, on one occasion it took several on and off attempts but it eventually came on.
Then there was the time last year when nothing worked so I called a serviceman. He came out opened the unit, checked wires, turned the switch on and off, turned the breaker on and off and nothing would work. He said that it was probably the Fan Blower Control Board or the Inducer Control Board, as he pointed here and there in the open unit. He said that he'd look into some prices for me and call the following day. He then put the bottom panel back on, pushing in the interlock switch and voila, the unit came on. He offered to continue but I told him to leave it on at least until the floor was warm. He said to call him if it happened again but not to switch anything on or off so he could possibly see what the trouble was. That was over a year ago. The heater worked fine for the rest of last year's heating season and has worked fine for all of this, until this morning.
I've found issues with this furnace, on this forum and other forums but not this problem (except there was a suggestion to check for fuses on internal boards being blown, which I did). As an aside, I bought both of the boards that he mentioned but never installed them. Still have them.
Does anyone have any suggestions? This time could it be one of the boards? Which one? Any troubleshooting tips? Any help appreciated.