Why Do Gas Furnace Control Boards Fail?

How Does a Gas Furnace Work

A bad control board is not uncommon a couple of times a week during a busy winter of service calls here in the Sacramento Valley. What are the parts on a circuit control board that fail, and why?

The printed circuit board of a furnace is the brains of the whole operation.  It’s the quarterback calling the shots down on the field of high and low voltage circuitry we work on every day.  On this week’s Fox Family Heating and Air Blog, we’ll talk about the parts on the control board that fail and explore some of the most common reasons why. 

What’s Failing?

So, what is failing on these boards?  A slice of silicon 10 years old should be the same composition as a 1-year old board, right?  It seems so.  Regardless, aging systems do begin to give more problems than the newer ones.

Printed circuit boards these days are composed of shrunk down relays and switches mounted on a rigid green board to orchestrate the sequence of operations that start up the furnace and gives us heat.  30 and 40-year-old furnaces we see still out in the field have these relays and switches.  They’re just bigger and sturdier because they’re made from more durable parts.

Last week we discussed how the smaller a control board gets, the weaker the material it’s made of.  The material is thinner, the solder connections are smaller, and the relays are made with tinier pieces of plastic and metal.

Control Board Life Expectancy

Our customers might think a control board should last the lifetime of the furnace.  And I’d say 50% of them do!  But all parts on the furnace control board have a life expectancy, and many things can happen to accelerate the aging process of the parts on that board.

Assuming there’s power to the board, it should function properly. If it’s not, there’s nothing we can do to bring it back to factory specifications.  You can’t make field solder connections right there on the spot that are going to meet any kind of standard the manufacturers set when creating the board.  Different soldering alloys will clash, resulting in a temporary fix at best.

Failed Solder Connections

That brings me to my first common failure on a control board.  I can’t tell you how many times I’ve talked about failed solder connections on the back of a control board.  Molex plugs have stems that are secured to the board and soldered in place to adhere to the metallic circuitry that act as wires do in a house.  If the wire has a beak in it, that circuit isn’t going to work. 

When the backsides of those Molex plugs develop a crack, it makes a gap between the stem that goes through the board to the backside where it meets the circuitry.  Any fractures in that solder connection are going to start creating intermittent abnormalities.  There’s a low voltage Molex plug and a high voltage plug that’s going to be a part of any furnace control we work on.

Thermal Expansion

You might ask, “What makes the solder connections fracture like that?”  Two words, thermal expansion.  Once the solder is applied and forms, it remains a very rigid metal with very little plasticity.  Warmth creates expansion.  And that kind of expansion within the solder joints is going to create a gap between it and the stem it’s supposed to be attached to.  This will cause problems with your boards either now or later. 

When I see a control board that has fractured solder connections on the back of the board, I let the customer know it doesn’t meet factory specs anymore and offer to replace it for them so they don’t have problems in the future.

Relays and Switches can Stick, Burn and Pit

Just like a contactor on the condenser outside, the control board at the furnace has miniature relays which allow certain motors to receive the voltage they need to operate.  And just like the contactor on the condenser, those furnace relays start to pit and burn from arcing that occurs across the contacts as they close.

High temperatures can melt the protective coating on the windings of the coil of a relay, which can prevent the contacts from closing in the first place.  Plastic pieces that the contacts are mounted to can lose stability with ambient heat surrounding the relay, too.  This can warp the contacts of the relay causing them to be misaligned and unable to function properly.

Stuck Switches

When an electro-mechanical switch like the ones on our boards is suddenly being used after a long period of downtime, like the end of one winter to start of the next winter, it can become permanently stuck.  Tapping on the relay can sometimes help, but only delays the inevitable failure of the board.

Over-voltage, like in-rush and other voltage spikes, creates constant overheating.  Under-voltage can prevent the contacts of a relay from staying closed securely.  And it’s not just the voltage that’s damaging these parts.  It’s also the current being carried with that voltage which wears out switches prematurely.


Transistors are typically the first part to fail in a control board.  Once again, the damaging heat and energy that hits those transistors due to voltage spikes, or even a little bit of static electricity, can wear out a board prematurely.  This is going to change the composition of the materials they’re made of.   Over time, they just give out, preventing the control board from working properly.

Power Surges

Asking questions with the homeowner can reveal a lot when diving into an HVAC system that isn’t working properly.  A recent thunderstorm or lightning strikes in the area can send a surge through the house’s electrical system.  That surge might not affect the lights or kitchen appliances in the house.  They may not even trip the breaker if the furnace is on at the main panel.  But it might take out the transformer before the board, sending a jolt to that sensitive control board.

Brownouts from the power company are notorious for damaging HVAC equipment.  A reduction in power that suddenly comes back on with no warning can damage the protective coatings on parts, causing them to fail either now, or even a couple years from now.

Another power surge a house can experience is a car accident in the area that may have taken out a power line. As the connections of those high voltage wires attached to the poles rip apart or get stretched, the influx of energy and the damage it causes happens instantly.  

Many HVAC parts have been taken out by these three situations, causing anywhere from a few thousand dollars’ worth of damage, to simply blowing a little 3-amp fuse on the control board.  No one should ever underestimate the freakish damage that can occur to an HVAC system when power surges happen in or around a house.

Static Electricity  

Careless or unsuspecting technicians who walk across a carpeted floor to get to their furnace can build up more voltage on the body than it can store.  As a result, that voltage will need to be transferred to the next piece of metal it comes in contact with.  You don’t want that to be the metal on a control board.  Electrostatic discharge (ESD) can even develop after you’ve grounded yourself to the furnace the first time.  Standing on a carpet can create that static very easily. 

The damage is done to the control board terminals when ESD hits the board.  There are very thin insulating layers within the control board’s transistors, relays, switches, and solder joints that will break it down.  What’s even worse is that sometimes that discharge won’t cause damage to the board immediately.  It’ll damage the insulation to such a degree that the device fails sometimes hours or even years later.

Control Board Degradation Over Time

A diagnosis of a bad control board is not an uncommon one.  But it makes me wonder what that board has gone through during its life to have gotten to the point where it’s now failed.  The parts themselves have an expected life span.  Everyone agrees with that.  But factors such as thermal expansion, power surges, and static electricity all play a big part in the degradation of a control board over time.

We’ve been getting excellent feedback from our fellow technicians like you who are out in the field working on this stuff everyday.  Please feel free to express your opinions and share your stories about failed control boards in the comments section below.  As HVAC techs, we’re always trying to learn, and there’s no better information than the lessons you’ve learned and can pass on to us.

Thanks so much for stopping. We’ll see you on the next blog post!

HVAC Training: 6 Ways to Prevent Damage to Printed Control Boards or PCB’s

How Static Electricity Kills Control Boards

Electrostatic Discharge is a Bigger Problem With Modern Electronics Than it’s Ever Been

When I first learned how to change a control board on a furnace, I was educated by my trainer to take great care in removing any static from myself before removing the board from the box.  He said I could damage the control board before the furnace even ran for the first time after the repair.  It’s called electrostatic discharge and it’s a bigger problem with modern electronics than it’s ever been.  This is what we’re going to talk about this week on Fox Family Heating and Air.

And for those of you who have experience handling control boards, let us know down below in the comments section if you have any other safety suggestions or any good war stories from your time in the field.  We’re always trying to learn as HVAC techs, and there’s no information better than the lessons you’ve learned and can pass on to us.

Reducing Electrostatic Discharge

About a third of all control board failures come from damage caused by electrostatic discharge.  You might have seen those pristine labs where they manufacture control boards.  One of the main goals for these rooms is to reduce static.  Once a control board is created, it’s prone to static damage.  If that damage were to happen at the lab the cost to manufacture another one is very little.  If the damage happens during testing it requires 10 times the cost to make it.  And if that board fails at the customer’s house, it takes 100 times the cost to manufacture a new board at the lab, package it, ship it to an HVAC warehouse, ship to the HVAC contractor, who drives it to the customer’s house, and has it ready for the customer to replace it, and put a warranty on it.

When it comes to static damage to a control board, it’s not so much about the voltage being transferred from you to the metallic parts of the board itself, but the resistance it incurs as it travels through pins, transistors, and other parts of the board along its path to ground.

The Shrink-Down

You’ve seen those big controls and relays that were used on decades-old furnaces.  They’re the same controls used today to direct the sequence of events that start the furnace and shut it down.  Anyone who has worked on an old furnace can tell you those relays and switches take up a lot of space in the control panel.   These days all those relays, transistors and switches have been shrunk down to the point that they now fit on a printed control board the size of a small napkin. 

Those old relays and other controls being larger than today’s parts were constructed with heavier materials.  That’s why they’re more durable over time.  The strength of the materials used to build small control boards is obviously not going to be as durable as those bigger, heavier parts.  You know the saying; “they don’t make them like they used to?”  Well, there’s something to that.

The Victim

A static discharge 20 years ago would have been harmless to those controls.  Today that same discharge through the board can result in catastrophic damage.   Transistors are often the victims of static shock to a control board.  But pins, brittle solder, and the silicon itself can all be deformed by the heat that travels through during a static discharge.

Damage like this can make a control for the blower motor, which is supposed to be off at a given time, to a blower that s always on now.  Or a safety switch that is normally closed to become constantly open.  These parts of the furnace that are needed to work in a certain order can be thrown out of whack very quickly with the slightest arc from your body to the control board.

Unseen Damage

Most people don’t even know they’re charged with static electricity as they cross the carpet floors and on to the HVAC system of a customer’s house until they feel the spark travel from their fingers to the brand-new control board they’re changing out.  Some of those techs also don’t know they’ve just damaged that expensive control board their customer is getting ready to pay for either.

You don’t have to be wearing a flannel shirt and your favorite pair of wooly socks to develop static.  Although clothing like that, as well as other situations, can create a significantly higher amount of energy than the body can store, which will need to be discharged at the next available piece of metal you touch.

Why Inspect?

Suppose you were out on a preventive maintenance or a service call doing a visual check of the backside of a control board.  We all know of the solder connections on the back of those boards which are receptors for a Molex plug that controls many of the basic functions of the furnace.  The heat from even a minuscule 24 volts, over time, will fracture those solder connections, which is why we inspect the back of the boards on a regular basis.  But if we bring with us a body full of static, and touch that control board, we can create a very minor defect in the board, or make a pre-existing, undetected condition even worse.  All of these fractures break down the control board over time until it completely fails.

Every control board I’ve changed was stored in an anti-static bag that comes inside a cardboard box.  Even those anti-static bags are conductive!  But they do help reduce and negate any static electricity the board might encounter during shipping and riding around in the back of your truck.

What Can We Do?

So, what can we do to prevent ourselves from damaging printed circuit boards in the future?

1. Ground Yourself

Do what my trainer told me to do.  Ground yourself to the furnace before touching the delicate components inside them.  Something that has a direct path to earth.  When we ground ourselves, we’re removing any excess voltage we may have created and carried with ourselves as we walked to the furnace.

2. Avoid Carpet and Rugs

Try working in an area where you’re not standing on carpet or area rugs.  These will encourage you to generate static even after you’ve already grounded yourself to the unit the first time!  A canvas drop cloth is less likely to generate that same static.  Working on bare or concrete floors is even more ideal.

3. Humidity Levels

I know you can’t change this while you’re servicing the HVAC system, but understanding the humidity levels in the room can help.  A room that has 40% to 50% humidity is less likely than a dryer room to encourage static.

4. Remove Voltage Potential

Make sure you’ve unplugged the furnace.  You want to make sure there are no electrical currents running through the system.

5. Handle with Care

When you do take the control board out of the anti-static bag, or when you remove one from the furnace to inspect it, make sure you are only touching the sides of the board.  Voltage potential is conducted through all the metallic parts of the board.  These are the areas you don’t want to have your fingers all over.

6. Stay Hydrated

Speaking of hands, keeping your skin moisturized by drinking plenty of water and even using lotion will help keep static-electricity down.  Dry skin encourages static to build up even after you’ve grounded yourself a first time.  You’re not off the hook as far as static discharge goes. Grounding yourself to the furnace multiple times is not unheard of.

Here’s a Little Tip!

Want to reduce the chance of that painful snap between you and the metallic object you choose to ground yourself to?  Use something like your metallic car keys to touch that ground.  This allows the discharge to travel straight through the key instead of going straight to your hand.


I hope this helps you with your question as to ESD damage to control board furnaces.  If you’ll take the time to ground yourself properly, you’ll reduce the chance of transferring the voltage to the control board.

Thanks for stopping by and we’ll see you on the next blog post!

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Should I Go to HVAC School or Get Hired as an HVAC Apprentice?

Trade School or Apprentice

People entering the trades question whether they should start their journey out by going to an HVAC trade school or by trying to get hired on with a company as an apprentice.  It doesn’t matter where you are in the world.  The answer to that will differ based on the company you’re trying to get on with, and what YOU want as a future employee. 

I think after reading this blog post you’ll have the confidence to start your way into the trades by figuring out this question.


My intention for this post is not to suggest whether you should or should not go to trade or vocational school to start learning your trade.  There are a lot of my audience reading this in a classroom right now.  And really, there’s nothing preventing you from doing both.  You can never have too much training and education.  In fact, my company offers continuous training on a weekly basis.  New information, best practices, and advanced technology are constantly updating in this field.

But if you’re reading this, you’ve decided that working in an office setting is not for you.  You’ve decided you want to work in a different setting.  One that changes on a daily basis.

An HVAC technician that learns installation and service is really diversified and becomes proficient at more than just HVAC skills, but plumbing, gas, electrical, construction, framing, aerodynamics, thermodynamics, roofing, structural engineering, etc.  Where are you going to learn all of this?

My Story

I was a mechanic in the air force after graduating high school, but I don’t think that really played much of part in my first company hiring me, other than I was manageable.  I went to a job fair they had and listened to their job descriptions and everything they had to say.  I deciphered that they really needed install helpers, so that’s what I told them I wanted to do. 

The next day they called me for an interview.  I went in with a polo shirt, jeans and some clean black boots, and breezed right through an interview that basically was held just to see how I spoke for myself.  It was more of a conversation to determine what kind of personality I had.  And, they hired me with no HVAC knowledge at all! 

I started learning how to install HVAC equipment, run gas pipes, line sets, handle high and low voltage, frame out a new return can, and how to run ductwork properly – all while getting paid, and learning some valuable fundamentals for later on in my career as a service technician.  I got some good overtime hours, and pretty much doubled my starting pay within a year.

But is it that easy for everyone?  It can be.

Going the Apprentice Route

Most local companies in your area provide either residential or commercial HVAC services.   Some companies do both.   It really seems like companies who value their employees have no problem training them, or paying for them to go to training after they’re hired.  The benefit to you as a person looking to work somewhere is, these companies get someone trained up the way they need them to be.  It’s also more efficient for you because it saves you a lot of money and you get trained for the job you’ll be performing.  So, you get your training in the classroom either at the shop you work at, or at a school they send you to.

I found most HVAC company owners I speak with would rather take on a new employee who doesn’t have any experience, but has a great personality, than taking on a skilled technician who has no class, can’t hold a conversation, or has no teamwork mentality.  The reason is that they can be trained in the way that the company wants them to be trained.

Early Spring

Bigger companies typically hire more techs per year than smaller companies.  So, if you’re looking to get on with a company, I tell people to start with the bigger companies around town.  Also, February to April, (early spring) is the best time to try because companies are looking to ramp up their staff to get ready for the busy summer season.  And that’s a great way to get on to prove yourself to the company that hires you. 

But I’ve heard that some of those big companies will also lay off folks when it slows back down after the summer.  And that really saddens me.  It’s got to be frustrating for those techs.  But I think everyone makes their own way where they work. 

My company and the company I worked at before don’t practice laying people off.  Some techs might lose some hours because their employer is slow and didn’t have the work for them, but either way, when it did slow down (like every HVAC business does during the off-season) my employer kept me busy because I was out there proving myself worthy of being on the clock every day.

During that first couple of years as an installer, working hard, staying busy, and getting the job done in a timely manner kept me busy all year.  That’s what employers like to see. 

The Facts About Trade School

There’s no such thing as too much education.  Look at the people who check out channels like mine.  It’s because they’re seeking more input about the HVAC field.

An apprenticeship you’ve been given can be shortened significantly with a degree you earn at a trade school.  Completing an organized class dedicated to the HVAC field is a huge help.  The teachers of those classes are typically seasoned veterans who have been out there and done that for years.  Getting the opportunity to learn from these experts is a great opportunity for you to learn and pick up some really good knowledge.

Getting Hands-On Training

Taking classes after you’ve been hired on deepens your understanding of the HVAC industry even more.  And going to a trade school puts you in a setting unlike a university because you’re not sitting in a big lecture hall.  Typically, these training centers have air conditioners, furnaces, heat pumps, ductwork, and other HVAC equipment already set up, so you get hands-on-training while going to class.  It won’t be the same intensity as learning it out in the field, but it’s a great start.

A lot of trade schools have connections with HVAC companies in your area, too.  So, it’s nice to have that in your back pocket as you approach graduation.  That’s the point of it all anyway, to have a job when you get out of school.

At a trade school, you get your degree faster than going to a university.  They will likely require that you take classes that may not have much to do with the HVAC field.  A trade school can get you in and out in about 6 months, which means you have a good start to finding your first HVAC job.

Entering the Real World

Once you do have your diploma, its time to go out and face the music.  Which is what you could have done rather than going to a school anyway.  I’m only saying that because the company that gave me my chance literally taught me everything I knew before going out on my own as an HVAC contractor.  But if you choose the route of getting hired on as an apprentice somewhere or if you graduate from school, you have to go out and find those companies.  You have to take the step to go face to face with the companies you want to work for.  Whether you choose to face them with a diploma in your hand or not is up to you.

Finding a Company

But there are definitely HVAC companies who will hire you right now, with no experience.  It just depends on where they are in their demand for technicians at the time you’re trying to get on with them.  If they’re not hiring, they’re not hiring and that has nothing to with you having a diploma in your hand or wanting to earn your way on with an apprenticeship.  I have had to turn down good people just because I didn’t have room on my team at the time.

Find some companies in your area that have a good reputation.  You can find them by looking at their reviews online.  Try these companies first, because they are doing something right.  They obviously take pride in their company’s practices, so they very likely care about their employees.

My Road to Success

I wanted a real job.  Being an HVAC technician has been the avenue which has gotten me to where I am today.  A husband, father, homeowner, and someone who can afford to go out and do the things I want to do with my free time.  I’m able to save money for my retirement and take care of my medical needs with the insurance I’ve been provided.  It’s a long way from the previous jobs I had which really didn’t offer these extras that a real job provides. 


Hopefully this has helped you on your way to deciding whether to go to a trade school or to try and go straight for an apprenticeship with your local company.

Please leave your comments down below and tell us if you went to school or not.  If you could, tell us how that went for you so those who are reading this can learn from your experiences.  See you on the next post!

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