My sister has an ancient Biltwel Gravity Furnace in her basement that just stopped working. For four years she has just jumpered the thermostat wires upstairs to run the furnace. (Thermostat face completely gone.) There are only two wires coming into the thermostat and NO 110 VAC.

In the basement, I can find NO 110VAC going into the unit. As a gravity unit, there is no blower. When I jumper the two thermostat wires at the gas valve, the unit still doesn't work.

What am I missing? What opens the gas valve if there is no 110VAC anywhere? What is my next step to get it working? The gas valve also has a pair of wires that goes up into the lit pilot light assembly.