I am actually writing for my sister with no internet. I do not have the model of the furnace. They came to their cabin today to find it frozen. The diagnostic light on the Nordyne Intertherm Furnace will flash twice when the furnace is turned on. The furnace will run for a few seconds and the shut off again. Could not find a manual anywhere with diagnostics in it on the internet either. Any help would be appreciated. Thank you.

It could be

Pressure Switch Stuck Open = 2 Flashes

How do you close pressure switch on nordyne furnace?

Remove tube and drain water if any is present. Blow in the tube to activate the pressure switch. If that does not work replace the pressure switch.

BTW turn off the power before you do this.