Thermostat Needs Adjustment

Problem: Thermostat works, but turns furnace on and off rapidly, causes major swings in temperature, or shows readings other than the setting.

Background: Normally, properly in stalled thermostats require little or no attention. However, some common problems can often be remedied by the homeowner, thereby saving the expense of a service call. If the thermostat has been recently installed, consult the instructions that came with the unit. For other thermostat problems, see
Thermostat Doesn't Work and Thermostat Malfunctions.

What to do: If the thermostat turns the furnace on and off relatively often, the problem is likely that the burner-on period is too short. Inside the thermostat is a heat anticipator lever which can be set to a range of scale markings. Adjust the lever one scale mark higher. Wait at least several hours for the thermostat to stabilize. If the thermostat allows major swings in temperature, the problem likely is a “burner-on” period that is too long. In this case, adjust the heat anticipator lever one scale mark lower. Again, wait several hours for the system to stabilize.

Special advice: If the thermostat set ting and the thermometer reading disagree, the thermostat may not be level, it may be affected by drafts or radiant heat, or it may be out of calibration. To check whether it is level, place a bubble level or a plumb line against the unit. If the thermostat is being affected by drafts and heat, it may need to be relocated. If it is out of calibration, read the unit’s instructions to find out how to adjust it, or call a technician.

Helpful hint: Normally a thermo stat should be placed at least 5 feet off of the floor, away from sources of heat (including sunlight), and on an interior wall. It should also be positioned away from corners and dead spots behind doors and in closets. It should not be located on walls that have ducts or pipes inside them, and should be protected from air flow within the wall. Plug any holes cut into the attic or crawl space for plumbing and wiring, and plug the hole behind the thermostat where the low voltage wires emerge.




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