Electronic Ignition Gas Furnace Problems Troubleshooting - Gas furnaces are a very popular form of heat for homes and businesses and occasionally a gas furnace needs to be repaired because of a problem with the gas furnace. Since there are many different types of gas furnaces it is difficult to cover every single possible gas furnace problem that can occur with a gas furnace in one article we are going to break this theme “gas furnace problems” down into series of articles with the first one being gas furnace problems with electronic ignition gas furnaces.
Electronic Ignition Gas Furnace Problem & Troubleshooting: Gas Furnace Sequence of Operation
The Sequence for Most Electronic Ignition Gas Systems
On most electronic ignition gas furnaces sequence of operation but not all the sequence will occur in the following manner:
Sequence of Operation - Electronic Ignition
- Call for heat at the thermostat. The house is cold and the furnace needs to come on to heat the house. The thermostat is the first part of the sequence of operation for the gas furnace.
- The thermostat completes a basic circuit for heating. This completion of the heating circuit in the gas furnace sequence of operation is a signal. A signal for the gas furnace control board to put everything into motion.
- The induced draft or forced draft motor engages. Some furnaces have either a forced draft motor and others have an induced draft motor. It depends on the engineering, The difference being the forced draft blower blows air through the heat exchanger(s). The induced draft motor pulls air through the heat exchanger(s).
- Above all, safety is key. The gas furnace control board checks the safety circuit to ensure all the safeties are closed as they should be closed.
- After safeties are confirmed to be good the control board sends a signal to start the ignition process. Depending on the type of electronic ignition the gas furnace the source of ignition will give a trial for ignition. You could have hot surface ignition, direct spark, intermittent pilot, or possibly some other ignition. See our article for electronic ignition gas furnace types.
- The trial for ignition includes a flame proving to ensure there is, in fact, a flame. This proves the gas is being consumed and not spewing into the environment. In that case, with no flame, the furnace would create an explosion hazard. Most manufacturers use the flame rectification method to ensure the flame is lit.
- Once the control board is satisfied that the flame is proven burning either it opens the main valve. The intermittent pilot lights the main burners. In the case of direct ignition, the main burner is already burning and the heat exchanger is heating up. The heat exchanger is getting ready for the next part of the gas furnace sequence of operation.
- The next step depends on the manufacturer the control board. Blower control is either on a timer or a temperature sensor. This will control the time when the blower will turn on. The reason for this is that the heat exchanger needs to warm up before the blower turns on. This is so that warm or hot air can be delivered throughout the supply ducts.
- Furthermore, the next step in the gas furnace sequence of operation is the thermostat is satisfied and shutting everything down. This happens with a small delay in the blower shutting down. This allows heat to be dissipated from the heat exchanger. The burners shut off immediately once the thermostat is satisfied. The blower continues usually on a timer. However, some systems do control the blower by the temperature in the heat exchanger.
- Lastly, the blower shuts down and everything is off and waiting for the next time thermostat calls for heat.
Standing Pilot Gas Furnace Sequence of Operation can be found here. The standing pilot sequence of operation is different than the sequence for the electronic ignition gas furnace.
Electronic Ignition Gas Furnace Problems & Troubleshooting
In any case, many things can happen in that furnace sequence of operation that can prevent the gas furnace from providing heat. Probably the first thing that can happen that will prevent the furnace from starting is the failure of the draft motor. In that case, the power to the motor, which usually originates from the control board should be checked. If that is okay then the motor itself needs to be checked.
For instance, a bad inducer or forced draft motor will prevent the pressure switch from closing. The pressure switch is in the safety circuit. If the safety circuit is not complete then the control board will stop the process of the gas furnace igniting. The gas furnace problem with the motor or the pressure switch needs to be corrected. Corrected before proceeding any further in the process of fixing the gas furnace problem.
Furthermore, another issue that can occur with the draft motor is the blower wheel. If the blower wheel is bad and not moving air then it needs to be repaired. Additionally, some manufacturers use eighth-inch rubber or plastic hose to check pressure for the pressure switch. If the hose is disconnected or dry rotted it needs to be repaired or fixed.
Electronic Ignition Gas Furnace Problems & Troubleshooting | Several Ignition Controls Are Available. Here is a sample
Another furnace problem to troubleshoot that is related to this is one of the safety switches being open. The pressure switch is a safety switch. However other safety switches include limit switches that can trip. They trip either because the switch is faulty and needs to be replaced or because there is a problem. A problem that is causing too much heat to build up and causing the safety limit to open. It opens to prevent damage from the excessive heat build up. Additionally, safety switches are very important and prevent catastrophe.
Lastly, all limit switches should be checked in the event of a gas furnace problem with a limit switch. Or a gas furnace problem in the safety circuit. A bad blower, dirty filter, collapsed ductwork, plugged up flue can cause the limit switches to open. All the gas furnace problems need to check out with proper troubleshooting techniques. All problems resolved before the furnace can be safely returned to operation.
Furthermore, the next most common problem for furnace troubleshooting that can occur is the flame sensor or flame rectifier. This problem can be observed when the intermittent pilot or the direct ignition of the main burners will ignite and then extinguish itself right away. The fire in the burners or pilot will extinguish after a slight delay. There is a flame. However, the flame sensor fails to recognize the flame. In this case, the flame sensor is probably fouled or dirty and needs to be lightly sanded to remove the invisible problem that is giving us this gas furnace problem. Proper furnace troubleshooting techniques can solve this issue.
Additional Common Issues
Additionally, another common problem that can occur with electronic ignition gas furnaces is that the igniter fails for whatever reason. In this case, it is prudent to check the ignition wire and the control board or control module where the spark originates. Do this to make sure it is activating the proper voltage to make the spark. Of course, this applies to spark ignition electronic ignition gas furnaces. However, not to hot surface igniters which is a different animal altogether.
Of course, the same applies to a hot surface ignition gas furnace as you check the voltage output from the control module or furnace control board which on most gas furnaces the voltage is 120 volts with a few being rated at 240 volts. Another exception being the Honeywell smart valve which is 24 volts to the small hot surface igniter which is located at the pilot light.
Hot Surface Ignition
Furthermore, on the hot surface ignition gas furnaces if the voltage output is there to the igniter it is possible the igniter is bad. To check the igniter you can Ohm it to make sure it has resistance. If no resistance is read (open circuit) then the igniter is broken or cracked and needs to be replaced.
It is also absolutely essential that any gas furnace ignition system has a good ground. A good ground to the control board or control module. This will ensure the 24 volts system is not a floating 24 volts. This means the 24 volts cannot float from one leg to the other. When a proper ground is done on the control voltage the 24 volts will not float. Rather, you will have the 24 volts on a single leg. This is what you need on the electronic ignition gas furnace controls.
Other gas furnace problems exist however these are the most common one can look for when troubleshooting. Later we’ll add some more gas furnace problems in this article. We will also have other articles in this series to help resolve problems with gas furnaces.
Electronic Ignition Gas Furnace Troubleshooting
Electronic Ignition Gas Furnace Problems Troubleshooting