If the high side thermistor was fused closed and the heater when off on high limit, the EGO switch, I would reset the switch. If the heater lights after that i would consider changing out the thermostors.
The low thermostor closes on temperature drop, thus allowing the heater to light. The high thermosotor opens on temperature rise, thus turning the heater off. The failure mode for the high side is not that easy to check.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles