I have a furnace, which worked well until today. The furnace fan/blower can be turn on manually (switching to ON position from the thermostat--Maple Chase 9600). However, when the fan switch is switched to AUTO position, and the room temperature is below the setting temperature, the furnace is on, but the fan/blower is not. What should I do?
By the way, the furnace and thermostat both are about 10 years old.
Thanks!

Likely on a 10 year old furnace the blower is controlled by a relay activated by the controls a short time after the controls get a signal that the gas ignited. Could be a dirty flame roll out switch, or a sticking relay.

Hi Labman,
Thanks very much. Another interesting thing is that when the fan switch is at ON (the fan is turned on), after I switch the setting temperature higher than room temperature, the furnace will be On, but the fan is turned off. What should I do?

It sounds like the heat-fan relay on the PC board is bad. You will need a new PC board. There are 2-3 relays on these modern furnace boards, one for heat, one for cooling and often a 3rd one for fan on.

Hi NorthernHeat,
Thanks very much.

My thermostate is working fine. The fan on the furnace turns on, the pilot light lights up, then I get a high pitch noise and everything shuts down?

I have a reguler natrual gas fernance and the burners go on and produce heat when the thermostate is turned up but after the burner shuts off the blower fan will not turn on what's the probem?