Knowledge is one thing that I love to share; whether it's about Jesus, cars, children, or my day job it does no good if you can't teach others what you've learned. However, knowledge is simply knowing something. Unless you apply it, it could be embarrassing at least and dangerous or deadly at worst. Customers and technician wannabes can get into serious trouble trying to diagnose and fix their own heating and cooling systems.
What really brought this into focus was a call one of my coworkers got last night. They declined for him to come over, but insisted that either the board or igniter had failed. A talk with the homeowner and her boyfriend confirmed this as I made my way to their home. I was there a year ago, and knew the furnace was on its last leg last time I went over there. It was 20 plus years old and had a faulty igniter (I noticed the customer replaced this part after my last visit). A little poking around the cabinet and I found that the limit to the vent had tripped and I immediately sensed trouble. I reset the limit and the furnace came on. As it did, the vent got really hot and I decided I've better get the combustion analyzer. The readings in the vent were over 350 degrees F for an 80% efficient furnace and the carbon monoxide level was over 50 parts per million. A check for carbon monoxide in the duct work was 15 parts per million, more than enough to be dangerous with exposure over time. 35 ppm is enough to give you a headache and dizzy in 6 to 8 hours, but any exposure will cause permanent damage over time.
I couldn't find any cracks at the heat exchanger and offered the customer to use our infrared camera (a $3000 piece of hardware) but she elected to replace the equipment. Any carbon monoxide over the furnace isn't good and from experience, not all heat exchanger problems are visible depending on the construction. I've had to fill some with water to prove a problem.
Lesson hopefully learned; unless you've been through some experience and training and do this for a living you may want to gracefully decline diagnosing this yourself. The gentleman who did this would have been swapping parts and the furnace still would have cut out. Worse yet, he could have tried to bypass that limit and really run into some problems where the outcome would have too grim to think about. I've been doing this for almost twenty-seven years and can't claim to know everything, or even come close. Between me and my employer we have over five thousand dollars per tech in diagnostic equipment and much training and knowledge to bear on a problem. A layperson trying to solve a problem is going be hit or miss at best. To put it another way, you wouldn't want me trying to settle a legal dispute, or performing open heart surgery as my results wouldn't even be fair to midland. Who wants fair to midland with legal or medical issues? You shouldn't settle for a mediocre result on your home comfort equipment either. Call a pro and have it done right.
Yes, I do offer fixes, but only after diagnosing and ruling out other issues that could put you and others at risk. I can't stress enough that you and you alone are responsible for applying knowledge in reasonable and safe manner. Besides, the internet is no substitute for a competent heating and cooling technician with the proper tools, knowledge and the wisdom to apply them in a given situation. Maranatha!