I've got a Ruud ultra series furnace and the coldest say on record since 1888 it starts shutting itself off and im now gettin 3 codes 13,12,46. Ive
What is the model number of the furnace? There are many "ultra series" models.
Also look on the back of the doors and let me know what it says besides Code 12, Code 13 and Code 46.
I think error code 46 has to do with the pressure switch.
Make sure there is no blockage in the drain line leaving the furnace, or outside at the vents.