I have a Comfortmaker Furnace (guessing 10 years old) with a Honeywell SV 9541 Smart Valve. Furnace would not turn on in Heat mode. Ruled out thermostat and inducer fan so changed out the Honeywell unit with another one. Previous Honeywell Unit hand solid Green indicator which does not match ANY error code. New valve has 3 Flash Error. As experiment, I powered the Inducer fan directly, forcing it on. After 20-30 seconds the furnace fires up, main fan comes on and furnace heats as normal - indicator light at that time has the constant flash indicating normal operation. After Wiring back to normal same result - no cycle, no vent fan, 3 flash error.