I am having problems with my Bryant natural gas forced air furnace. It is electric ignition but does not stay lit. I have turned the temp up to 90 and flipped off the power switch at the unit. When turning it back on it lights for 1 minute and then turns off. I thought the flame sensor might be bad so I changed it. Still it will not stay on. I don't know if its the thermo coupler or if this model has a thermo coupler. The model number is 383KAV036111I am confident I can change this piece if I can find where it is. Thanks in advance for any help you can give me.