Lennox model GMP075-3.
Installed in '95.
I've tried resetting according to instructions on access cover panel (turn heat to 'off', turn off power to furnace, turn gas valve to 'off' for 5 minutes, etc.)
When I call for heat, small (induction?) fan runs for a few seconds, the igniter unit glows orange/white, but there is no flame.
After 3 cycles, the unit shuts off.
I've seen a red light on a circuit board flash a few times, then return to a steadily-lit status.
(Sorry, I don't know how many times the light flashes.)
I get the impression that no gas is getting to even one of the three burner units.
Ideas?
Thanks much.

GMP075-3 is a Goodman not Lennox model number. Have it inspected by a pro and have him figure out the problem for you. See my other posts on Goodman furnaces. P.S. be prepared to buy a new furnace if you call in the pros, it's better than a trip to the hospital though.