My thermostat is set at 50 degrees but the heat is pumping out at 76. I think it is broken.
Is is fairly easy to replace a standard wall mounted thermostat? And would this fix the situation?

Does it ever cut off? If you lower the setting on tstat,does furnace cut off?
Try removing red wire from tstat, with power turned off to furnace,after removal turn power back on
Does it stay off or start back up?(with red wire disconnected)

Let us know what happens