I recently bought a home that's approximately 12 years old. The gas heater seems to be working fine, but no flame. I can smell gas, but it never shuts off unless I turn it off.

A few months ago I had a similar problem where the sensor needed to be cleaned. The problem then was produce a flame, but shut down after 10 seconds... producing no heat. This is not the case now. I did clean the sensor again just to make sure. But, that sensor, I believe, is the safety mechanism to shut down the system if it does not sense a flame. This is not happening. The system still continues to run.

I am not a technician, but I read the schematic. There is a roll-out switch, but I cannot see if there is a reset. I have turned off the system a few times thinking that anything like that might reset to normal.

Check the sticky at the top of the forum. It includes an easy check of furnace/thermostat bad?

I'll take a look, but the thermostat is fairly new (months old).

I ended up replacing the igniter. Apparently, these things go out in 2-4 years. You just have to know not to touch the "rod" on a new one or you may shorten its life span.