On Jan 25, 2:49 pm, "Jimi" wrote:
. . . .(snip). . . Is there a thermostat to kick the
burners off in the event the heat exchanger reaches a critical temperature
. . .? Thanks for any replies...Jim

Yes.

My furnace has two devices, a low draft detector and high firebox
temperature detector.

The high firebox temperature detector failed and shut the furnace down
six years ago. The repair guy said they do that now and then.

Jason