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Thermostat Not Working?

Here are some tips to try to get the right temperature

FH99DJA_THERST_01-2Family Handyman
Does your house have to get really cold before the furnace kicks in, even though your thermostat is set to 68 degrees? You might need a new thermostat. Or it could be as simple as leveling your existing thermostat and adjusting its thermometer and anticipator. Here's how.

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Adjusting the thermostat

Photo 1: Adjusting the thermometer

On the backside of the thermostat, directly behind the mercury switch and coil on the front, you’ll find a small metal nib (some models have a slot for a screwdriver). Use this to adjust the thermostat’s thermometer, using a regular thermometer as a guide.

Photo 2: Level the thermostat and adjust the anticipator

Be sure the thermostat itself is level. To adjust the anticipator, remove the thermostat cover and look for a scale with the word “longer” on it and an arrow. Move the anticipator in small increments. Test each adjustment before making another one.

If your house has to get really cold before the furnace kicks in even though the thermostat is adjusted to a higher temperature, you probably don’t need to replace your thermostat. You just need to adjust the existing one, following three simple steps: (1) adjust the thermometer; (2) level the thermostat; and (3) adjust the anticipator.

To adjust the thermometer, remove the thermostat from the wall. On the backside of the thermostat, directly behind the mercury switch and coil on the front, you’ll find a small metal nib (some models have a slot for a screwdriver). Using a regular thermometer as a guide, adjust the thermostat’s thermometer. If you have a rectangular model, make sure it’s level when you replace it on the wall.

The anticipator controls the length of the on/off cycles of your furnace. For maximum comfort and efficiency, the anticipator should keep the temperature of the room from varying more than two or three degrees. To adjust it, remove the thermostat cover and look for a scale with the word “longer” on it and an arrow. If your furnace doesn’t come on unless the room is really cold, you’ll need to make the cycles shorter so the furnace will come on sooner. To do this, move the anticipator, in small increments, in the opposite direction of the arrow.

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Needle-nose pliers

You’ll also need a flat-blade screwdriver and a torpedo level.