The thermostat does not screw in. I rests within the Thermostat Housing.
i have a model 125u19 payne furnace i move the thermostat but nothing comes on in the furnace and the pilot light is lit
Call a mechanic
Remove the air inlet duct tube. Remove the heat shield from the exhaust and move it out of the way. Unbolt the crossover exhaust pipe bolts from the from the front exhaust pipes move it out of the way. Unbolt the thermostat housing pipe and remove the thermostat. Installation is reverse.
Thermostat
The pointer on a thermostat moves when the room temperature changes. This change in temperature causes the thermostat's sensor to detect the difference and adjust the pointer accordingly to indicate the new temperature reading.
usually you follow the upper radiator hose to the engine you have to remove that hose and the thermostat is between the hose and engine block....sometimes you have to move the alternator to get there
Loosen the alternator bracket, move it out of the way. The thermostat is at the end of the upper radiator hose where it curves into the engine
use the factory installed call an auto parts store and they will tell you the right thermostat you should be using
First locate the lower radiator hose, that hose should lead you to the thermostat housing (just behind the motor and to the left). This hose should be the same size as the top radiator hose. Second you move the clamp (pliers will work) down the hose away from the thermostat housing, then loosen that hose from the thermostat housing. Third you take of the 2 Bolts off from the thermostat housing, they should be 10mm. Remove the thermostat. When you replace the thermostat you may also need to replace the gasket. Simply put the bolts back in and tighten them, then reattach the lower radiator hose and move the clamp back to its original position. Note: The top radiator hose does NOT lead you to the thermostat housing!
you call then SIR or MA'AM and move on
Your thermostat might be stuck open