Modern furnaces are complex machines with various components and parts linked to their brain, the furnace control board. Like human brains, it controls EVERYTHING your furnace does. Thus, making furnace control boards a very essential component in every furnace.
It controls and operates all key functions, in the order, they occur in a heating cycle, for your furnace to perform and deliver its purpose.
Types of Furnace Control Boards
- Simple Ignition Control Board Module
This type of control board is commonly used in older models together with a fan control board. It controls the gas valve, the spark generator or hot surface ignitor, and the flame sensing circuit.
- Integrated Furnace Control Board
This type is what is generally used in modern furnaces. It is the combination of both the simple ignition control board and the fan control board. Thus, it works like a simple ignition control board. Still, it has extended features like onboard diagnostics and furnace blower control in both the air conditioning and heating modes.
Control Boards Sequence of Operation
- The heating cycle begins when the thermostat calls for heat
- The control board sends a signal to the draft inducer motor to start.
- The pressure switch senses a drop in pressure caused by the draft inducer motor and closes to complete a circuit. It also ensures the furnace’s exhaust is removed to the outdoors before the burners are ignited.
- The hot surface igniter then receives a signal and begins to light and heat up.
- After a few seconds, the gas valve receives a signal that clicks and releases gas to the burners.
- The burners then ignite as gas is released.
- The flame sensor senses the flame and sends a signal to the control board that a flame exists. The control board then allows the gas to flow to the burners, heating up the furnace.
- If no flame is sensed, the control board signals to turn off the gas valve and shuts down the furnace to prevent a gas explosion
- The rollout switches checks for irregular or oversized flames and flames outside the burner area. Then, it sends a signal to the control board for it to shut the furnace down.
- The limit switch then signals to the control board that the furnace is warm enough to turn the blower fan on.
- If the furnace is getting too hot, a signal is sent to the control board to shut off the burners and the furnace.
- If all is in place, the furnace blower motor then turns on, moving air through the furnace, removing heat and sending it into the house.
- Once the desired indoor temperature is achieved, the thermostat tells the control board. Then, it sends a signal to shut off the gas burners, the draft inducer motor, and the blower fan motor.
Furnace Control Board Troubleshooting
Furnace control boards do not only help in your furnace’s operation and heating cycle. It also assists in diagnostic the furnace problems. LED lights are usually visible through a tiny window on the furnace door that flash in codes to indicate a problem.
The flashing lights will show the number of blinks between pauses corresponding to a particular problem, as shown in a chart located on the inside of the panel lid.
Signs of a Failing Control Board
Since furnace control boards are complex electronic devices, they are common to fail and be replaced. Here are some common signs that your control board is failing:
Too Hot or Too Cold Temperature
A faulty control board can send late or early signals, resulting in some components working too long or stop working too soon. Hence a too cold or hot indoor temperature is set in the thermostat.
Irregular Heating Cycle Sequence
With a faulty circuit board, there might be some irregularities in the operation of the heating cycle. Be keen to observe if some components involved, like the draft inducer motor, gas valve, or burners, stop suddenly or continue to work. Which is different from the proper heating cycle sequence.
LED Light Diagnostic
As mentioned above, LED lights on the control board indicate a problem and what the problem is. In addition, a board or wiring problem will also be indicated there.
Furnace Control Board Replacement Cost
Once you have identified a damaged furnace control board, it must be dealt with immediately to not put your furnace’s operation in jeopardy.
The first thing you have to do is to find a proper furnace control board replacement which you can do by finding the manufacturer’s part number or the furnace model and serial number.
The price of a new furnace control board starts from $50 and may range up to $250 depending on your furnace model.
The average cost for an HVAC technician to install and replace furnace control boards is $400-$600.
Control Board Replacement, A Step By Step Guide
Furnace control board replacement does not take a lot of skill. If you choose to do the replacement yourself, here is a quick guide you can easily do:
- First, make sure to turn off the furnace.
- Take note of all the connections and mark where each wire goes on the old board. You can also take a picture with your phone as a reference.
- Then, remove the wires, screws or plastic clips and the board.
- Attach the new board with the screws or snap it in with the plastic clips.
- Carefully reconnect the wires, noting their correct placements, to the proper terminals. Check the wiring from the photo taken.
- Run the unit and verify that the heating cycle sequence is properly done.
If you are not comfortable doing the above mentioned steps, do not hesitate to call a professional HVAC technician to help you out. Also be sure to get the correct replacement board.
While DIY repair is possible, it’s best to call in an HVAC professional when your control board starts act some problems. It’s important to get it installed in precisely the right way. Often, professional equipment is also required to properly repair or replace your furnace control board, so it functions at its best.