Remove the thermostat cover and check for problems
1 of 2
Photo 1: Check level
Use a bubble level to check whether the subbase is mounted evenly on the wall. Tighten the mounting screws
when it's level.
2 of 2
Photo 2: Move the anticipatorIf the furnace is cycling on and off too often, move the heat anticipator adjustment lever arm closer to the "longer" setting by one calibration mark. If the room temperature is either too hot or too cold, move it away by
one calibration mark.
If you have a mechanical thermostat and your gas- or
oil-burning furnace cycles on and off a lot, or
the room gets too hot or too cold before the furnace
kicks on, you may be able to fix the problem
with a couple of simple adjustments.
First, remove the thermostat cover and make
sure the subbase is mounted level on the wall. If
it’s not, the mercury switch inside won’t work
properly, which can affect the accuracy of the temperature
readings. Your subbase will either have
leveling posts where you can lay the level, or a flat
area at the top or bottom where you can set the
level (Photo 1). Move the subbase around until it’s
level and then tighten the mounting screws.
Next, adjust the heat anticipator, which fine-tunes
the point at which the thermostat turns off
the furnace burners. Locate the heat anticipator
adjustment lever arm (Photo 2). If the furnace is
cycling on and off too often, move the lever
away from the “longer” setting by one calibration
mark. If the room temperature is either too hot or
too cold for long periods, move the lever closer to the “longer” setting by one calibration mark.
Let the furnace run for two to three hours and, if
necessary, repeat the above adjustment. If the
problem persists, you may need to replace your