I have a brand new Gibson (Nordyne KG7SK-072C-24B) Gas Furnace that was just installed two days ago.

After less than 24 hours, it stopped providing any heat, but instead blows only cold air. The blower will not shut off unless I turn off the electrical disconnect for the entire system.

The supply side has a brand new filter, and does not appear to be blocked.

The AC coils were cleaned during installation; the air flow out of the vents seems normal, and none of my vents are blocked.

There does not appear to be any blockage in the exhaust vent system.

What are the other possible causes of this?