More complex furnace control boards will also have control over the blowers and/or the built-in diagnostic system.
To simplify things, you can think of the furnace control board as being a driver and the furnace as its car. Just as the driver oversees all the functions and operation of the car from ignition to shutting off the engine, likewise does the control board for the furnace.
A typical operation sequence for a furnace control board goes something like this:
- The control board receives a signal from the thermostat that the temperature is too low.
- It starts the ignition system, whether that be a spark generator, glow coil or pilot light.
- Once the ignitor is hot, the furnace control board initiates the flow of gas through the burners, where it is ignited.
- The control board keeps the furnace running until it is signaled by the thermostat that the temperature is now high enough, or until it detects something is wrong.
(An example of a malfunction where the control board would get involved is a thermocouple that is not detecting enough heat. In this case, the control board would shut off the gas flow to prevent a leak into the home.)