Control Boards and Furnaces 101

A furnace control board is essentially the computer, or the brain, in a furnace. It operates the key functions in the order that they are supposed to happen and controls everything from turning on the gas to shutting down the fan after your home has reached your desired temperature. While it is a very essential piece to your furnace it is common for control boards to be replaced.

TYPES OF CONTROL BOARDS
There are two types of control boards for gas furnaces. The first is a simple ignition control board module, which is more common in older, less efficient models. It controls the gas valve, the igniter and the flame sensing circuit. These older units will have a fan control board along with the simple ignition control board. Control board

The more common control board, at least in newer units, is the integrated furnace control board. This controls the same things as the simple ignition control board but it controls the furnace blower as well. Ultimately it is the simple ignition control board and the fan control board in one.

STEP-BY-STEP SEQUENCE
To understand whether or not your control board is operating correctly, it is first imperative that you understand the step-by-step sequence of your furnace, which should be like this:

1. The thermostat is set and calls for heat.
2. The induced draft motor turns on.
3. The pressure switch senses a drop in pressure and closes to complete a circuit.
4. The control board sends a signal to the hot surface igniter and the igniter lights up.
5. Then a few seconds later the gas valve clicks and releases gas to the burners.
6. The burners ignite in sequence.
7. The flame sensor senses the flame and allows the gas to continue to flow, heating up the furnace.
8. The blower motorturns on and moves air through the furnace to keep it from overheating.
9. The limit and rollout switches remain closed and continue to monitor the airflow.
10. Once the thermostat is satisfied, the control board shuts off the gas.

TROUBLESHOOTING
The control board can also help you diagnose a problem with your furnace. Most control boards have LED lights that flash to indicate a problem. The different flashes serve as codes. Follow the chart on your control board to decipher what the flashing code means. The code might tell you that you need a new control board.

Control boards also have lights to let you know that it is on and functioning correctly. If this light is not on, then the control board can be reset by turning off the furnace power and restarting it. However, this is not normal; a control board should not have to be reset.

CONTROL BOARD REPLACEMENT
If you find that you need a new control board, HVACPartsShop.com can help you find the correct replacement part. Use our furnace model drop list to select the correct control board using your furnace model number. You can also use the manufacturer’s part number to find the correct part. If you are still having problems figuring out which control board is right for your model you can use our online chat feature to chat with a certified technician or you can call us at 1-866-215-3831.

When you begin the replacement, please first make sure that the power to the furnace is off. Before removing the wires make sure that you have marked them so that you know which connection they go to. Then remove the wires, screws or clips and the old board.

Attach the new board and carefully reconnect the wires to the proper terminals. Then restore the unit and run it through a complete cycle, verifying that is follows each step of the sequence.