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Electronic Ignition Gas Furnace Problems Troubleshooting

White Rodgers Gas Furnace Ignition Control Board

Electronic Ignition Gas Furnace Problems Troubleshooting - Gas furnaces are a prevalent 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 a 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

There are different levels of problems that can occur with any gas furnace. The most common failure is electronic ignition failure. That is quite common with gas furnaces. Knowing how to troubleshoot a furnace problem is key to solving the problem. Another common fault is a failure of electrical systems on a gas furnace. Both of those failures can be the same. Consequently, that is an electronic ignition failure can be the result of an electrical fault in the system somewhere.

And when I say electrical failure with a gas furnace problem, I am speaking of controls. Or control wiring with the gas furnace. To break it all down, we begin with the sequence of operations with a gas furnace. Furthermore, this is very important to understand if we are to troubleshoot the electronic ignition gas furnace problem.

Gas Furnace Troubleshooting Electronic Ignition Systems

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:

Gas Burners for a FurnaceSequence of Operation - Electronic Ignition
  1. Call for Heat
  2. Control Board Initiates
  3. Induced Draft Motor Turns On
  4. Safety Circuit Check
  5. Ignition Process Begins
  6. Flame Proving
  7. Main Burners Fire
  8. Blower Control Initiates
  9. Thermostat Satisfies Setpoint
  10. Shutdown Sequence

1

Call for Heat

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.
2

Control Board Initiates

The thermostat completes a primary 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.
3

Induced Draft Motor Turns On

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).
4

Safety Circuit Check

Above all, safety is vital. The gas furnace control board checks the safety circuit to ensure all the safeties are closed.
5

Ignition Process Begins

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 gas furnace, the source of ignition starts 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.
6

Flame Proving

The trial for ignition includes a flame proving to ensure there is, in fact, a flame. That 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 burning.
7

Main Burners Fire

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.
8

Blower Control Initiates

The next step depends on the manufacturer of the control board. Blower control is either on a timer or a temperature sensor. That controls the time when the blower turns on. The reason for this is that the heat exchanger needs to warm up before the blower turns on. That is so warm or hot air is delivered throughout the supply ducts.
9

Thermostat Satisfies Setpoint

Furthermore, the next step in the gas furnace sequence of operation is the thermostat is satisfied and shutting everything down. That happens with a small delay in the blower shutting down. That allows heat to be dissipated from the heat exchanger. The burners shut off immediately once the thermostat is satisfied. The blower usually continues on a timer. However, some systems do control the blower by the temperature in the heat exchanger.
10

Shutdown Sequence

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 prevents 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 prevents the pressure switch from closing. The pressure switch is in the safety circuit. If the safety circuit is not complete, then the control board stops the process of the gas furnace igniting. The gas furnace problem with the motor or the pressure switch needs to be corrected and 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 an eighth-inch rubber or plastic hose to check the pressure for the pressure switch. If the hose is disconnected or dry rotted, it needs to be repaired or fixed.

troubleshooting manual reset limit switch

Manual Reset Limit Switch

Safety Switches

​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. Switches 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 excessive heat build-up. Additionally, safety switches are critical 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 is returned to operation.

Flame Sensor

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 ignite and then extinguish itself right away. The fire in the burners or pilot extinguishes 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.

Furnace Limit Switch Safety

Safety Limit Switch

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 too 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

hot surface igniter

Hot Surface Igniter - it will glow red hot when in the ignition mode

Furthermore, on the hot surface ignition gas furnaces, if the voltage output is there to the igniter, the igniter may be 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 essential that any gas furnace ignition system has a good ground. The module needs good ground to the control board or control module. That ensures the 24 volts system is not a floating 24 volts. That means the 24 volts cannot float from one leg to the other. When it has a proper ground, the control voltage, the 24 volts, does not float. Instead, you have the 24 volts on a single leg. That is what you need on the electronic ignition gas furnace controls.

Conclusion Electronic Ignition Gas Furnace Problems Troubleshooting

Other gas furnace problems exist; however, these are the most common ones that can look for when troubleshooting. Later we’ll add some more gas furnace problems in this article.

Additional questions from our readers:
How do I know if my furnace ignitor is bad?

This depends on what type of electronic ignition you have in your furnace. Probably the most common ignition failure is:

  1. the flame sensor is fouled. This will prevent the furnace from providing heat. It is a safety feature for the furnace. Clean it but be very careful cleaning it. A very fine grit sandpaper or a wire brush will do it.
  2. The next most common ignition problem is a cracked hot surface ignitor. Replace it.
  3. The next problem is a wildcard. Check any furnace flash codes if the furnace is so equipped.
Can I light the pilot manually if the furnace is electronic ignition?

The short answer is no. See another article we wrote on this topic. Lighting a pilot for electronic ignition?

What causes furnace ignition failure?

The answer to that is extentively explore in this article along with other articles in our gas furnace troubleshooting category.

Electronic Ignition Gas Furnace Troubleshooting

High Performance HVAC

Electronic Ignition Gas Furnace Problems Troubleshooting

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