Failed Furnace Control Board: How To Check And Replace It

Blog author image
Mark Jardine
April 18, 2024
Heating & Cooling
Blog post image
The HVAC circuit board of your furnace serves as the heating system's brain, instructing the complete model on distributing heated or cooled air throughout your house. Because smaller boards often have weaker materials, different sizes might affect their age and durability.
Circuit boards are used by furnaces for various tasks, from lighting your heating system to warning you of a problem with the furnace itself. In a perfect scenario, the AC board would last as long as the main furnace, eliminating the need for replacement. Nevertheless, they are prone to failure, so you must be ready to make repairs.
Another pricey repair is replacing an AC panel board. However, a variety of factors might make it less useful. Voltages and surges can impact the circuit board's ability to function. A circuit board can malfunction due to dirt, as dirt and dust can accumulate and create an insulating layer that traps heat, causing the aircon panel board to overheat and burn out.

What's Failing?

Several different factors can lead to the failure of a furnace control board. Although they can last the entire lifespan of a furnace, control boards can malfunction. What, then, is not working on these boards? It should be the same for a board that is a year old and a slice of silicon that is ten years old, right? So. Nevertheless, older systems do start to have more issues than younger ones.
Modern printed circuit boards choreograph events that ignite the furnace and provide heat by being made of miniature relays and switches on a hard green board. These relays and switches are found in the 30 and 40-year-old furnaces, and they are more robust since they are constructed of better materials.

Control Board Life Expectancy

An A/C control board should, and occasionally does, survive as long as the furnace itself in an ideal world.
However, different elements of a furnace control board are affected differently as people age, and any one of them might eventually stop functioning properly.
Any universal circuit board repairs are temporary fixes because of the standards the manufacturers use while making these circuit boards.

Parts That Usually Fail

Any complicated electrical device may malfunction in a variety of ways. Although they are intended to be sturdy, control boards can only sometimes survive the whole lifespan of a furnace. Here are some parts and signs of a bad furnace control board.
  • Damage from power surges. Even if a power surge in your home doesn't knock out the lights, it might damage the transformer in the furnace control board or blow its fuse.
  • Stuck relay switches. Miniature relays on the control board are used to power various components. These relays may develop a stuck open position and refuse to shut due to contamination, a loss of their protective coating, or warping that causes misalignment. Electro-mechanical switches in older furnaces have a chance of being jammed permanently.
  • Failed transistors. Your system may have issues if the starting capacitor is failing. A cheap solution to the problem is to replace the capacitor.
  • Loose wiring. Your furnace shakes and rattles each time it is turned on and off because of the movement. Internal wires may become so worn out with time that it causes a short. Finding the loose wire will solve the issue quickly. An examination and tune-up performed regularly can assist solve this issue.
  • Wrong fuse. Have you experienced this issue even after having another HVAC service specialist check you? It's possible that the technician provided subpar service. They may have installed a fuse that was inadequate for your system's capacity.

Steps for Checking Your Furnace's Control Board

You'll need a few specific tools to test your AC circuit board troubleshooting. It would help if you had a voltage meter. The furnace won't function if the door switch is up because the makers believe it is hazardous to operate a furnace with the access panel off. You will also need electrical tape to tape down the furnace door switch and a screwdriver to remove the access panel. It has a pop-up switch, just like the fridge's light. Here is how to test a furnace control board. Step one is to check your control board after gathering the required tools.
  1. Take Down Access Panels. Remove the access panels for your furnace using your screwdriver. The control board is usually located at the base near the blower.
  2. Inspection using sight and smell. Some control boards appear to have been damaged. For instance, you could notice burn scars or faulty wiring, indicating that the entire board has been blown. Use your nose if you can't see any damage.
  3. Check the diagnostic lights. A diagnostic light on your control board can let you know if problems have arisen. Many furnaces feature a window or port made of plastic or glass with an LED light or lights within. To signal an operational fault, the lights flicker sequentially. Calculate the number of blinks and consult your handbook to identify the issue. If the indicator light is off, there is no power to the control board. The lights may display "low voltage" as an error code, which might mean that your control board is malfunctioning.
  4. Check your power. Check whether your furnace has a door switch to check the electricity entering your control board. To prevent electrical mishaps, tape this switch down. Find the standard wire joining your control board from your transformer. You should observe 120 volts on the voltage meter if everything is operating.
  5. Terminal testing. If electricity does reach your control board and the indicator light blinks, you must check the thermostat connections. Connect and test the terminals with your furnace off, turning them back on and off between checks.

How To Replace a Furnace Control Board

A furnace and AC board replacement is a rather tricky procedure that those with the necessary expertise should only carry out. If you insist on replacing the control board for your furnace by yourself, proceed as follows:
  • Cut off the furnace's electricity. Turning off the electricity is a crucial initial step since you'll work with wiring and electrical circuits within the furnace.
  • Open up the furnace. Depending on the furnace model, you might need to remove other parts to access the control board. Once you have a good view, kindly snap pictures of the control board and its wirings. The photos will come in handy when you attempt to reconnect things later.
  • Disconnect the control board's wires. All different kinds of cables and wires connect to the control board. Remove each one to ensure no further connections to the board.
  • Take the furnace's control board out. Remove the control board from the furnace once you have disconnected all the cables. One or two screws are often used to secure the control board.
  • Install replacement control board into the furnace. Installing the new control board is now necessary. This is an excellent time to set up if your control board has dip switches or jumpers. Adhere to the switch/jumper configurations on your old control board. The replacement control board should be screwed into the furnace in the same manner as the previous one.
  • Reconnect wires to the new control board. It's time to link everything at this point. Use the old control board from your photos as a guide (you did remember to take images, right?). Reconnect all cables and connections to the new control board.
  • Close up the furnace. Reassembling everything is now necessary! Remember to put everything back together if you have to disassemble anything else to get to your control board. Please put all of your furnace's access panels back in place to shut them down.
  • Turn the power back on and test. Finally, the decisive moment. Reconnect the electricity to your furnace, then check the thermostat to see whether it works.
Your furnace's control board may malfunction if you find that it is turning on and off at odd times, isn't responding to thermostat adjustments, makes a lot of clicking noises, or the blower won't stop operating. We advise turning off the furnace and giving us a call. Avoid attempting to manipulate the control board yourself! It would be best if you didn't try to repair a gas furnace unless you're a skilled professional.

Who Should I Call For Furnace Repair and Replacement?

Problems with a furnace can be annoying, mainly if they occur at inconvenient times. Several factors might be challenging to identify and treat. But the issue can be avoided with little tender loving care and routine maintenance.
The first step is to determine the precise part that fits your furnace type, whether you need to replace the circuit board, the igniter, the flame sensor, the vacuum switch, or a fan motor in your furnace. This process is made simple by Home Alliance. We have authentic replacement parts to use for all your repairs and replacement services. For all the top heating and cooling services, Home Alliance has the solution for it. Contact us and book a service with us! We also do air duct cleaning and replacements. Check out our other blogs like this duct replacement guide.