The thermostat,water level and all else are fine. It never over heats and once the heat finally kicks on it works like it should. Fan works fine,defroster and lots of hot air until the system cools it down somewhat depending upon the temp selected. It’s in a sensor or computer that is slowly malfunctioning. Right in the owners manual it tells you the fan will not come on for up to a couple of minutes upon start up on a cold day and that’s what it used to do. Now it’s coming on later and later IF it ever comes on.