Cardinal Gas Heater Issue

[Jealxndr]

Question regarding the furnace in my Cardinal. Just at the conclusion of winter I noticed my heater would fire up and upon reaching the set temp shuts off...and never turns back on again. Almost as if the thermostat shuts off (it doesn't) I have to turn the stat off for a minute and back on in order to get the furnace to fire up again. And then it does the same cycle again, reaches temp, shuts off and never fires up again. I have purchased a new Thermostat, but it comes with a 'modulator' or manifold or something to where I am afraid to jsut swap it out without hearing from someone else who has experienced something like this. Anyone have any suggestions?