The inducer fan motor starts,the hot surface igniter heats up and the gas valve opens producing a nice blue flame for 3 or 4 seconds and the gas valve shuts off. There are no red flashing lights to indicate a problem with any components. This unit was built around 1993. Any ideas on what might be wrong?

My first thought is a dirty flame sensor. It is a thin silver rod that sits in front of the burner on the opposite side of the ignitor, remove, and clean rod with sand paper, reinstall. Be sure to shut the power off to the furnace.

I got the same problem with this. The flame came on for about 5-10 sec and keep cycle for about times and then everything stops. The LED flash one that indicates ignition, gas flow, gas pressure.. Please help me out as well before I call the service man.. Thank you very much.

Same problem... Took out flame senser, used very fine sandpaper to clean, put the senser back in, works perfectly.. FYI. Thanks hvacservicetech