I have a Tempstar natural gas furnace with a Honeywell Contoller (SV 9541). Sometimes when the furnace comes on, the gas will come on but not ignite, which causes the system to go into a safety lockout. Any guesses what is up? Additional Info: Furnace model N9MP1075B12B1 (as far as I can tell - it is hard to read) We have some sort of Smart sensor igniter, which might have been replaced last year, and we go through control fan timers at a rate of two or three a year. Any help is appreciated.