Why is gas furnace sequence of operation important? If a technician is to properly troubleshoot a gas furnace he needs to know the proper sequence of operation for the particular gas furnace he is troubleshooting. In gas furnace troubleshooting I believe the most common gas furnace to fail is the gas furnace that never gets regular preventative maintenance performed. In most cases you will not need to troubleshoot a gas furnace if regular maintenance is performed. An annual check of the gas furnace by a professional HVAC technician will help you avoid many problems that arise in gas furnaces during the heating season when you really want to rely on your gas furnace. So the best advice is to get your gas furnace a maintenance check and tune-up at least yearly so you will not have to worry about spending any time during the colder months in a cold house and worrying if your pipes are going to break and so and so forth. It is truly hazardous to your health and your dwelling not to have a reliable gas furnace so make sure you get regular gas furnace maintenance.
Additionally you need to understand the basics of gas furnaces. If there is any doubt what-so-ever it is best to call a professional and let them troubleshoot the gas furnace. After all, we are talking about fire and a gas that can explode. When in doubt leave it to the professionals to troubleshoot your gas furnace. A professional understands basic electricity and electrical components and controls, different types of gas systems and these gas systems functions, and all the necessary things to be wary about or look for to stay safe whenever they are troubleshooting gas furnace systems.
First you need to know what kind of furnace it is that is having issues and then you really need to know the sequence of operation for the gas furnace if you are to properly troubleshoot the gas furnace. Knowing the sequence of operation will help in troubleshooting a gas furnace as most HVAC technicians know in any troubleshooting scenario the gas furnace sequence of operation is important when troubleshooting gas furnaces. Below I will run through a few different scenarios for gas furnace sequence of operation so you will understand the importance of knowing gas furnace sequence of operation when troubleshooting a gas furnace.
The standing pilot gas furnace is the most basic of all modern gas furnaces and while they are slowly being replaced with newer electronic ignition gas furnaces the standing pilot gas furnace still remains in some homes so it is necessary to troubleshoot a standing pilot gas furnace from time to time. With most standing pilot gas furnaces you will two major components in the gas furnace that will need to be checked for problems. The air side of the standing pilot gas furnace consists of a blower motor, a few safety controls, and the blower motor control. The gas side of the standing pilot gas furnace consists of a gas valve, a pilot assembly, the pilot and main burners, and the flue which exhausts the gases after the combustion process is complete. The sequence of operation for the typical standing pilot gas furnace goes like this:
1. A call for heat from the thermostat
2. The main valve in the gas valve energizes provided none of the safeties are tripped
3. Provided the pilot light is lit the main burners fire and begin heating the combustion chamber
4. As the combustion chamber heats up the fan limit control slowly heats up until it reaches the cut in temperature for the blower
5. The blower kicks on and runs continuously
6. When the thermostat is satisfied the main burners turn off
7. The blower continues to run to dissipate extra heat out of the heat exchanger. When the temperature reaches the cut out setting on the fan limit control the fan stops and the heating sequence of operation is complete
In the standing pilot gas furnace sequence of operation there are many things going on and a good technician will follow the sequence through to determine where the furnace has a fault and make the repair.
There are many different types of electronic ignition gas furnaces in use today. There some that are proprietary to various manufacturers and then there are some manufacturers that use another manufacturers controls for the electronic ignition part of the gas furnace. Trane gas furnaces are an example of a company that makes their own electronic ignition gas controls for their furnaces. For this reason when you troubleshoot an electronic ignition gas furnace you not only need to understand the sequence of operation for various electronic ignition gas furnaces but you also must understand how the controls work. A good technician can walk up to an electronic ignition gas furnace and figure out basic problems with the gas furnace in a few minutes. Of the different types of electronic ignition gas furnaces there are direct fired gas furnaces and indirect fired gas furnaces with the indirect fired gas furnace using a pilot light and the direct fired gas furnace using total main burner ignition without a pilot light. The key in both systems is that each electronic ignition system has its very own method of proving the flame or proving the fire exists. If no fire exists then the system shuts down to prevent gas from being spewed into a space where it can become very hazardous.