What Causes a Furnace Circuit Board to Burn?

If your furnace stops working and a professional repair technician discovers that the issue is in the circuit board, your first question will likely be, "what causes a furnace circuit board to burn out?" You'll also wonder whether the issue is repairable.

Although many circuit boards last for the life of the furnace without any problems, board failure is common. In many cases, circuit boards stop working because of small issues that worsen over time without you realizing it until the furnace stops working. When that happens, repairs may be as simple as replacing faulty electrical components or strengthening wiring connections, or a total control board replacement may be the only solution.

As Bozeman's professional furnace repair experts, Premier Systems can quickly diagnose problems with the circuit board and recommend solutions. If your furnace is not working, call us at (406) 629-1583 for help from one of our experienced technicians. In the meantime, keep reading to learn more about common issues and causes of burned-out circuit boards.

What Is a Circuit Board?

Even if your furnace burns gas or oil to produce heat, it also uses electricity. The furnace circuit board, also called the control board, is essentially the "brains" of the furnace. Not only does it control the ignition, ensuring the furnace turns on when needed, but it also controls critical parts like the fuel valves, blower, and flame sensor; in some systems, it also controls the air conditioning functions. 

The Most Common Reasons Furnace Circuit Boards Fail

The furnace circuit board has several important functions, meaning it must withstand significant wear and tear. Control boards are durable, but their complexity makes them vulnerable to failure. Knowing what causes a furnace circuit board to burn can help you troubleshoot and identify the cause of your furnace issues. 

1. Age 

The older your furnace, the more vulnerable it is to malfunctions. Time takes a toll on any appliance, and as the years pass, vibrations, thermal expansion, power fluctuations, and general wear and tear can cause the furnace circuit board to fail. Taking steps to reduce ongoing stress on the furnace, like regular maintenance to inspect and clean mechanical components, can help protect the electrical circuit panel and extend the furnace's lifespan.

However, if the circuit board fails due to age, the best solution may be to replace the entire furnace rather than just the circuit board. The furnace may continue to have mechanical breakdowns that require repair, making a replacement the most cost-effective solution.

2. Wiring Issues

When the furnace runs, it creates vibrations that can loosen wires on the control panel. Loose wires create electrical shorts, which can cause the breaker switch to trip. If this keeps happening, or the furnace won't come on even if the breaker switch is in the on position, loose wiring could be the cause. 

An HVAC technician can adjust and tighten the wires on the panel to solve the problem and keep the furnace running reliably.

3. Power Surges

If lightning strikes your home or you experience a power surge for any reason, it can burn the furnace circuit panel. You may not even realize the damage if everything else in your home works properly, but a surge can destroy the furnace control board. Power fluctuations during a brownout can also affect the furnace circuit panel and cause it to burn out.

In either case, technicians cannot repair damage to an electrical circuit board from a power surge, making the only solution a total replacement. 

4. Relay and Switch Issues

Furnace circuit boards have small relays and switches to control power flow to the system components. When these switches become stuck, the board malfunctions and can burn out. 

Circuit board switches can wear out faster than they should if the power voltage to the board is too high or too low. The switches may also fail due to accumulated dirt, corrosion, or warping from improper alignment. Whatever the cause, a technician may temporarily correct the issue by tapping on the relay to release the switch or cleaning the circuit board, but more often than not, a new circuit panel is necessary.

5. Transistor Problems

Transistors typically fail due to electrical voltage spikes or static electricity. Excess electricity changes the part's material composition, causing premature failure. 

In older furnaces, time and wear and tear cause transistor failure. In fact, furnace panel transistors usually fail before any other parts, ultimately causing total board failure. Technicians can't replace failed transistors, so the who board will require replacement.

6. Faulty Solder Connections 

Furnace control boards have metallic circuitry that works like wiring in your home to direct electricity flow and control various functions. The circuits connect to the board via Molex plugs, which have stems soldered to the back of the board to hold them in place. If the solder cracks, it causes a gap between the stem and the circuitry, ultimately keeping the board from working properly. 

Repairing the solder to eliminate the loose connection can restore proper function.

7. Thermal Expansion 

Sometimes, what causes a furnace circuit board to burn isn't a defect but rather the result of normal function—thermal expansion is one of those regular occurrences. It can cause solder connections to fail and create abnormalities in the electrical current that keep the furnace from working.

Solder is a rigid metal, but ongoing exposure to heat can cause it to expand. When the metal expands, it can create gaps in the electrical circuit stems. The ongoing process of heating and cooling can also make solder brittle and weak over time, further disrupting the normal electrical currents. 

In most cases, technicians can replace the solder to restore strong connections and solve the circuit board issues. However, if the existing solder is especially brittle or if making repairs will keep the circuit board from adhering to code or manufacturer standards, a technician may recommend replacing the circuit board to prevent future problems instead. 

8.  Static Electricity 

Sometimes, a well-meaning homeowner or HVAC technician can accidentally damage the furnace circuit board with static electricity. Walking across a carpet, for example, can increase voltage buildup on the body. If the first piece of metal you touch is the circuit board, that electrostatic discharge—static electricity—can damage control board terminals, often immediately. 

Even if it takes a few hours or weeks for the static electricity damage to appear, it is permanent. If it occurs, the only solution is a new board, so it's critical to discharge all accumulated static before touching the control board. 

Turn to Premier Systems for Help with Any Furnace Problem 

It's very common for furnace control boards to have problems or even fail. If the switch on the circuit breaker is on, but the furnace does not seem to have power, then the circuit panel likely needs repair or replacement. You might be able to determine the specific issue if your furnace has a panel that shows error codes.

The licensed experts from Premier Systems have the knowledge and experience to identify what causes a furnace circuit board to burn and solve the issue to restore reliable heat. Scheduling repairs at the first sign of the problem can prevent it from getting worse and ensure your home and family remain warm and safe. If you think something is wrong or have questions about how often to service your furnace to prevent a burned-out circuit board, schedule an appointment today with our team in Bozeman, MT, by calling (406) 629-1583.