Furnace does not kick on until ambient temperature drops 6-8 degrees below programmed temperature. Once the furnace kicks on, it warms the house nicely. Honeywell programmable thermostat was just changed last night and was not the problem. Diagnostic lights are blinking #1 slow and #2 fast (according to manual it is low flame signal). Is this normal operation? Is the problem most likely with the furnace or thermostat or somewhere in between?