Blower & burner don't stay on... I think it's some kind of thermal switch...

Exhaust blower starts... ignighter glows... gas valve opens and burner lights... main blower starts...

It runs for about 3-5 minutes and then the burner abruptly shuts down... another 1-2 minutes and the blower shuts down... desired temperature not reached.

Please help! It's cold in my house.

Thanks!

Check your air filter
Have you chenged the thermostat lately?
Need complete and exact model number of unit.