When it is extremely cold outside your thermostat will be set to a very high temperature. Your furnace will cycle on and off about every 10 minutes or so. A furnace that turns on and off too much is more than an annoyance, it drives up your utility bill and is in need of a heating repair. The following is some answers to this common problem

Thermostat Problems

If your thermostat’s heat anticipator has gone bad, this may cause frequent cycling or the turning on and off too much of the furnace. The heat anticipator is an electrical resistor device mounted in the center of many mechanical thermostats that fine tunes the point at which the thermostat turns off the furnace burners. It consists of a simple thin wire mounted to a disc which is attached to the bimetallic coil. It anticipates the flywheel effect of a space heating up and turns off the burners a short period of time before the space reaches the desired temperature.

To adjust the anticipator:

First, remove the thermostat cover and make sure the subbase is mounted level on the wall.

When the heat anticipator is out of adjustment it can cause the furnace to exhibit symptoms of short cycling (turning on and off frequently) or to exceed or never reach the desired thermostat heat setting.

To adjust the heat anticipator perform the following steps:

  1. Remove the thermostat cover
  2. Make sure the thermostat is level. If it is not level the mercury switch will not work properly.
  3. At the center of the thermostat find the small disc with calibration marks as shown in the photo above. It will probably have the word “longer” on it. The disc will have fastened to it a lever arm and indicator relating to the calibration marks. This is the heat anticipator adjustment lever arm.
  4. If the furnace is cycling on and off too frequently, move the heat anticipator adjustment lever closer to the “longer” setting by one calibration mark.
  5. If the furnace is exceeding or never reaching the desired set temperature, move the adjustment lever away from the “longer” setting by one calibration mark.
  6. Once the appropriate adjustment is made let the furnace run and the temperature stabilize for a period of 2-3 hours.

If necessary, repeat the above procedure.

If the problem persists and you cannot resolve the problem with these steps, you may need to replace the thermostat.

Dirty Air Filter

During the winter months, a furnace’s air filter can become clogged with dirt, dust, and other particles. Once the pores of the filter are blocked with this debris, the heated air flow will be restricted because it can’t pass through the filter and into your home duct system. Because much less than the standard heated air reaches your home’s rooms, the thermostat will keep calling to turn the furnace on. To fix this problem, locate the furnace air filter and replace it. Make sure that when you remove the old air filter, pay attention to which way the arrow is facing.

Blower Motor Problems

A problem with the furnace’s blower motor may cause the heated air to slowly reach the areas in your home. The blower includes a motor, belt, and motor bearings. A worn out or cracked belt, an old or bad motor, or loss of lubrication within the motor are all causes for the inefficiency of the furnace to cycle on and off properly.

Thermostat Heat Anticipator Description


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Richard Marton Electrical Contractor LLC is a full service electrical contractor serving homeowners and businesses in Bergen, Passaic, Essex and Morris County New Jersey with electrical installations and repairs. We are also a Generac Generator installer.

Richard Marton Electrical Contractor LLC works with general contractors, residential architects, interior decorators, interior designers, painters, property management and property maintenance professionals, and professional organizers. We work with these professionals to give clients top of the line electrical installations within such projects as residential remodeling, residential renovations, plus build outs of new kitchens, bathrooms, home offices, add-a-level residential project and more.

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