Thermostat inoperative damaged parts missing The inspector will indicate an inoperative thermostat if a condition exists that implies the thermostat could not possibly operate, such as parts missing, etc. Inoperative thermostats usually need replacing. Thermostats are inexpensive and can usually be replaced by the property owner without professional help. Several types of thermostats are readily available at all building supply outlets especially the home improvement type stores. Installation instructions are normally provided with the units. Being loose or unlevel could cause some thermostats to operate incorrectly due to a mercury containing vial which depends on its position to turn the unit off and on. Loose thermostats can usually be tightened by carefully opening or removing the cover of the thermostat and tightening the screws that mount the thermostat to the wall. If they are stripped, try removing them and set the thermostat slightly away from the old placement and reset the screws. Inaccurate thermostats are common. Once the inaccuracies are calculated, you should be able to set the unit to a usable setting.