Sometimes (its happened three times, twice in last month) the heater is not kicking on. After we trip the fan-auto switch back and forth the heat will come on. It is an janitron thermostat-not digital--more than 6 years old. Gas furnace, also probably more than 6 years old. Could this be a thermostat problem? Is it something to be concerned about?

Thanks!

Little problems ignored may get worse. When the heat doesn't come on, is it the gas too, or just the blower? The gas should come on a little before the blower. If the blower doesn't come on, the gas will go off again. It may cycle several times and then shut off for a while. If that is what it is doing, it may be the relay or timer that controls the blower. Unfortunately they are both on a circuit board and very difficult to identify and repair. I hate to say replace the circuit board.

One other check would be to jumper the red and white wire to the thermostat at the furnace. Likely you can see them when you open the panel to change filters. Just run a little wire from one to the other and put the panel back on restoring power to the furnace. If it starts right up, the thermostat or wiring to it is bad.