If your furnace is under 20 years old, chances are that you have what is called an “integrated control board.” What this means is that it has a little red and sometimes a green led light attached to the control board. On this Trane furnace shown above, it is a single, red led and can be seen by looking through the little window on the bottom door. This is known as a fault code light or diagnostic code indicator light. When there is an issue with your furnace, you can take a peek through that window and take a look at this light, count and take note of the number of flashes. The number of consecutive flashes will correspond to a specific fault in the system causing the unit to shut down.
Once you have taken note of the number of repetitive blinks from the led light, you can now take the door off the front of the furnace. Next, you will need to find the diagnostic code chart. In the particular case of this Trane furnace, it was found on the control board itself as shown in the photo above. In other cases, however, it will be located on the inside of the bottom, blower compartment door.
Now that you have found the diagnostic indicator code list, you can go ahead and match how many flashes you had and see what the code shows. Let’s say the code was 1 flash. According to this, it would mean system lockout. This means that the system has attempted to start several times and failed. It then locks the system out for 3 hours before it will try again. If this was your case, it didn’t help you very much! What you do next, will help you.
You reset the code by shutting the power off to the unit and turning it back on. Be sure to put the door back on or hold down the door switch or the furnace will not power back up! It should attempt to restart now and if it fails again, it will blink a new code. Take careful note of this code as it will steer you towards the actual issue.
It should be noted that this indicator will only give you a vague understanding of the problem and could have several components covered under the same diagnostic code. You will need to do some investigating to find the real culprit and if you can’t figure it out, just use the Fixmyfurnace.com Virtual Diagnostic tool to help you through the process and get you what you need to get back up and running quickly and save you a lot of money!.