The heat anticipator essentially consists of a small disc attached to the bimetallic coil of the thermostat. The disc has a thin wire on its surface an d an adjustable arm that touches the wire. The position of the arm determines the electrical resistance of the wire, which in turn affects how hot the wire gets. As the wire heats up, it warms the bimetallic coil, which in turn shuts down the gas burners early, according to the heat anticipator’s setting.
The function of the heat anticipator is to fine-tune the point at which the thermostat turns off the furnace burners. Ideally, it turns the furnace’s burners off a short time before the room reaches the desired temperature. This is to compensate for the fact that furnaces cont inue to produce and distribute heat for a short while until the heat exchanger cools down. If the shut-off is properly timed, the room temperature edges up to reach the precise desired temperature shortly after the burners shut off.
When the heat anticipator in your thermostat is out of adjustment, it can cause the furnace to "short-cycle" (turn on and off frequently) or to exceed or never reach the desired thermostat heat setting. Fortunately, this problem is often easy to correct by adjusting the heat anticipator.
While you won’t be directly touching any live wires during this process, it’s always a good idea to turn off the electrical power at the main supply panel (breaker box) before executing any task involving electricity. If you don’t know which specific breaker cuts the power to your thermostat and heating system, you may want to turn off the main breaker, which will cut power to the entire house.