OK. So we fire up the heater this year ( a couple of weeks ago), and it comes on, no problems. We run it for a few days then shut it down. So today I go out to fire it up - no go. Under normal running conditions, I start the heater, the fan come on, 30 seconds later the "HEATING" light flashes on the control panel, the ignitor lights up, a few seconds later "floom", the heater fires up and we are in business. Today, when I turn the heater on, the fan starts like it should, but after the 30 seconds the "HEATING" light does not come on, the unit runs a few minutes, shuts down and flashes the diagnostic code "AGS", automatic gas shutdown. Now this thing is 8 years old, a little noisy, but otherwise seems to run year in and year out. I have had to replace the hot surface ignitor a few times, but when that is the problem the heater will flash the "HEATING" light, it just won't fire up. This one is a little different in that the "HEATING" light does not come on. Anyone have any ideas. Much thanks.