How Do I Know If My Furnace Control Board Is Bad? (Telltale Signs)

With all of the components within a furnace, it only makes sense that some of them will wear down and simply stop working eventually. Being able to recognize the signs of failure and implement a fix can save thousands in the long run and even keep your furnace working for far longer.

You can tell that your furnace control board is bad if there is thermal expansion or if the soldering connections are faulty. Bad transistors can also explain why a furnace control board isn’t working properly. Errors in sequences and worn or missing parts can also point to a bad furnace control board.

Before we look into the reasons why it isn’t working properly, it is important to know just what the furnace control board does. The control board is responsible for a series of operations that are essential to the furnace running at all, let alone efficiently.

It is responsible for opening the gas valve, starting the electronic ignition, activating the blower, checking the burner unit, venting the heat exchange, and shutting off the gas. All of these stages eventually lead to providing you with heat. The board going down for any reason can prevent the furnace from working at all.

While we can identify the things going wrong with a control board, why is it failing at all? After all, silicon that is a decade old should be made up of the same composition as a board that is a year old. So where is the problem?

Essentially, most printed circuit boards today are made up of shrunken switches and relays on a rigid, green board. The problem is that the smaller the board is, the weaker the material. When the material is thinner, the relays can wear down easily and stop functioning properly. And that is the essence of why most control boards stop working.

The most common failure in your furnace control board is in bad or failed solder connections at the back of your board. There are plugs with stems that get soldered into place to the metallic circuitry, acting as wires would in a house. When there’s a break, the circuit won’t work.

Should the plugs start to develop a crack, there is a gap between the stems at the backside where they meet the circuitry. Fractures within that solder connection create abnormalities (like the furnace not working, for instance).

The transistors are generally one of the first components within the control board that start to go. The heat and energy that gets created by the startup process can damage several components. That energy and heat will hit the transistors and can wear the board out earlier than expected.

That heat and energy damaging the transistors will eventually totally change the composition of the underlying materials. With enough stress and damage to those components, they will give out and the board will stop working properly.

For the most part, boards will have some kind of LED light to indicate when there is an issue during operation. Should your furnace stop running normally, try opening up the access panel to see if there are any red warning lights.

On most models, there should be a diagnostic chart somewhere on the panel lid’s interior. That chart will explain what your warning light indicates. Should you decide to call a technician, use this information to give them a better idea of what the problem is.

Under normal circumstances, your furnace should comfortably control the temperature in your home. Should you notice that your furnace is making things either too cold or too hot, start by checking the thermostat.

If that is fine, the problem could be that the control board is turning off certain components too soon or letting them run for too long. Even though there are a few different things that can cause this problem, the control board tends to be one of the usual suspects.