My thermostat, which has always displayed at 187f while moving, suddenly started dropping as low as 182f and then would go back to 187f. took it out and put it pot of water on the stove, heated it up and watched it open. let it cool and watched it close. It was sticking! It would open, stop, and then pop open a little more. Same thing happened as it was closing. Did this with the new tstat and it was a very smooth movement from full closed to full open and back. put in the new tstat and all is right with the world again.