It's a Suburban Dynatrail NT-30SP.
At the thermostat there is only one blue wire. AT the right side of the furnace are two blue wires coming out, connected to a red and white that go off to the left.
Wa8yxm, exactly what do you mean by this:
"Check Thermocouple to control board wire, DISCONNECT (Both ends one at a time) and re-connect a few times to clean the contacts." Would that be the two blue wires coming out of the side of the furnace?
And, where is that control board?
Old-Biscuit, at the thermostat there one each green, brown, red, blue, yellow and white wires. And, I can't see where to disconnect unless I need to pull that board out of the switch.
BTW all of you, thanks for taking the time to help me with this. It's warmed up a little here but it's fixing to get a lot colder.