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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: Understanding 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 the 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.
The Sequence for Most Electronic Ignition Gas Systems
Electronic Ignition Gas Furnace Problems and Troubleshooting
On most electronic ignition gas furnaces sequence of operation but not all the sequence will occur in the following manner:
The Sequence of Operation - Electronic Ignition | Electronic Ignition Gas Furnace Problems and Troubleshooting
- Call for Heat
- Control Board Initiates
- Induced Draft Motor Turns On
- Safety Circuit Check
- Ignition Process Begins
- Flame Proving
- Main Burners Fire
- Blower Control Initiates
- Thermostat Satisfies Setpoint
- 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 operations 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. A flame sensor that touches the flames when the burner ignites takes care of this issue. A single wire runs from the flame sensor to the ignition control board or module.
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. This process 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 | Electronic Ignition Gas Furnace Problems and Troubleshooting
Lastly, the blower shuts down, and everything is off and waiting for the next time the 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.
Manual Reset Limit Switch
Safety Switches
Electronic Ignition Gas Furnace Problems Troubleshooting
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 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, you should check all limit switches in a gas furnace problem with a limit switch. Or a gas furnace problem in the safety circuit. A bad blower, dirty filter, collapsed ductwork, the 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 are resolved before the furnace is returned to operation.
Flame Sensor
Electronic Ignition Gas Furnace Problems Troubleshooting
Furthermore, the next most common problem for furnace troubleshooting is the flame sensor or flame rectifier. This problem can be observed when the intermittent pilot or the direct ignition of the main burner ignites 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 gives us this gas furnace problem. Proper furnace troubleshooting techniques can solve this issue.
Safety Limit Switch
Additional Common Issues
Electronic Ignition Gas Furnace Problems Troubleshooting
Additionally, another common problem 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 is the Honeywell smart valve, which is 24 volts to the small hot surface igniter located at the pilot light.
Hot Surface Ignition
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 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 Frequently Asked 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:
- 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. Very fine-grit sandpaper or a wire brush will do it.
- The next most common ignition problem is a cracked hot surface ignitor. Replace it.
- 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 extensively explored in this article along with other articles in our gas furnace troubleshooting category.
The electronic ignition is not doing anything except flashing a light. What is the problem?
It is likely in the lockout mode as discussed in this article. Wait at least 30 minutes and then reset it by turning the power off to the furnace. Wait a few minutes and restore the power. It will go through its cycle and if something is incorrect it will shut down again. Many of these ignition control boards or modules will flash a code. To learn about gas furnace ignition control flash codes see this article.
Electronic Ignition Gas Furnace Problems Troubleshooting
Electronic Ignition Gas Furnace Problems Troubleshooting
I have an older furnace with Honeywell control (S86000H) and Honeywell (VR8204A 2027) gas valve. The system works well, but occasionally the ignitor shuts the sequence down due to lack of gas for the pilot orifice. I can’t measure the voltage to the gas valve, my meter (Fluke) shows random numbers, not any steady value at the pilot connection of the gas valve. (The ignitor spark tries to ignite but no gas come out of the orifice and the system shuts down after 90 seconds since there is nothing to ignite). A few minutes (or several tries) later everything is back to normal, and the system works fine. I suspect the gas valve (since the control box executes the sequence correctly) but have no information of the method (and correct values to be measured) neither on the control, nor at the valve. (The valve has separate circuits for pilot and main gas). Please advise!
My furnace will light and then turn off after 3-7 seconds. Flame sensor and control board are both new. Upon resetting the system it may run fine for one cycle only, but then will not restart with a new call for heat. Pressure switch and limit switches have all been tested and function. The board shoots off an error code for low flame sensed. The flame is on the flame sensor during the start up. Any thoughts?
Without looking at it I couldn’t tell you exactly except to check the basics. Make sure the unit has good ground and proper voltage ratings.
Ive got a carrier gaspack unit LP M3 48SD-030060301 with the gas ignition control board. I installed an ICM 291 board and a Hall affect sensor and I am getting a code#5 and directly after a code #6. I have amped out the inducer motor and it comes on right after calling for heat and reads .2 and the capacitor for it reads 4 mfg. Does not try to ignite at all. Carrier tech support says bad board. What do you think? Thanks in advanced
bad board
“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.”
Actually, if it’s bad (open circuit) it should have infinite resistance. A closed circuit gives you no or low resistance.
Thank you for clarification……………..an open circuit will read “OL” on an Ohm meter.
I have an American Standard Freedom 90. The inducer fan comes on, power comes to the ignitor (which works) for about 3 seconds and then stops and the furnace blower just comes on. Any ideas? Thank you.
Its something in the safety circuit such as a pressure switch or limit switch. Sorry to be vague, but without troubleshooting it with a multimeter I really can’t define the exact problem.
I have a 2 1/2 year old Luxaire HE furnace. It worked fine the first year, but started acting up the second year. Would not light and went into lockdown. Had furnace man come out and look at it. All he did was change the filter (Ihave to admit, it was pretty dirty). Everything worked fine up until this past January 2019.
Now the furnace will light for a few seconds then go out and try again. It will either come on the right way or it will light one burner and go out after 3 seconds. Sometimes it will light one burner, then the second one lights, then they both go out.
I have had 3 different repair companies, 4 different repairmen look at it and it still won’t work right. One repairman is still coming out weekly trying to figure it out.
Flame sensor has been replaced. New gas pipe and valve have been replaced. Johnson Control technician hasn’t been much help. Numerous electrical tests have also been done.
Please …..any suggestions would be gratefully accepted.
Check manifold pressure, make sure burners are clean, test gas valve for proper pressure drop, make sure the unit is properly grounded, test inputs/outputs on the board/module, check sensor position, get a better HVAC company with trained techs.
I have trying to fix my Lennox gas package unit furnace for three days. First repair attempt was to clean spark ignitor ground connection and it fired right up. The next time the thermostat called for heat it failed. The inducer was turning and I could hear the relays and gas valve clicking but no fire. I ordered a new ignitor and installed it. Still no fire. I noticed the sequence of clicks were no longer taking place either. I jumped the pressure switch and got the LED light to come on the ignition control and the sequence clicks and the brief gas odor from the exhaust for the attempted pilot ignition started to occur again but still not spark. I used a heavy wire the was grounded to see if was getting a high voltage spark from the ignition control and I can’t see any sign of a spark when the lighting sequence is taking place with the gas turned off. Could the pressure safety switch be connected to and other switches that prevent the spark?
Never, ever, ever, jump the pressure switch. It’s dangerous. Sometimes you got to throw in the towel and call in a Lennox technician. Of course, it could be the pressure safety switch and on recent models, engineers have designed the systems to sense when the switch is jumped out to prevent people from jumping them out. Why? See the first and second sentence. There are a few ways of properly testing a pressure switch and you need tools for the testing. A multi-meter and a pressure testing tool that measures in “inches of water column”. Then you need to know the pressure needed to throw the switch. Whatever the bellows is rated for. Somethings are better left for professionals for safety reasons. It’s safer and you’ll likely be warmer.
Recently replaced the surface ignitor switch.. .worked fine for a couple days, then required a slight ‘knocking’ on the furnace to get the igniter switch to turn on (get hot) while the fan was successfully running.
My luck (and the knocking) has run out…and now the fan is running but the ignitor refuses to come on. Help?
Not sure about this without looking at it. Perhaps one of technician readers will have a suggestion.
Thanks for the response – follow-up question. I ended up replacing the surface ignitor switch. This seems to have fixed the problem for the most part.
However, about 50% of the time after turning on the furnace – it only blows cool air. That is, until I gently ‘knock’ on the furnace, which 9 time out of 10 seems to fix it, and the ignitor turns on, gets hot, etc.
So why would the ignitor come on only 50% of the time? and why would me knocking on the furnace, or lightly wiggling the wires, seem to fix the problem each time (and enable the ignitor to get hot)?
I have the same problem with my boiler…I wiggle the wire and it ignites…I have to prop the wire a certain way at the board area (even though the wire is tight in the board)…so far so good as long as the prop does not let the wire move, my boiler is ok.
furnace comes on, but the ignitor is not heating up and turning color at all. when i switch the thermostat off the furnace does not turn off, until i flip a switch off on the furnace.
Sounds like a limit switch is popped. Check airflow first to make sure the airflow is good and if not fix that problem. If it does not the call a service company to find the exact problem……………….maybe a bad limit.
This is a Mr HeaterMaxx 50 000 BTU, it start but the middle burner does not start or work like old ford T puff several time and if it does not light the heater go on a lock down, What puzzle me the first and the last burner operate normally but the middle one is erratic. Any suggestion?
You likely have a blocked manifold or spud on the manifold. Insects can cause this problem.
Hi. I have an old Weil-Mclain gas furnace with White-Rodgers direct spark ignition. (White-Rodgers 5059-21 24V pilot relite control). Sometimes it wouldn’t spark and the heat won’t come on. The annoying thing is when you think it’s broke and I’m about to call someone, I turn it on and I hear the clicks and the flame is on again. Basically, it randomly clicks (sparks) and randomly doesn’t. What do you think is the problem? Do you think I need to replace the electrode or the whole relite control? Thanks.
It could be anything ie bad ground, flame sensor, weak output, gas pressure, gas quality and there really is no way to know without troubleshooting it to see what the problem is.
I have a Honeywell gas furnace it has two problems first it will light and then shut off right after that secondly sometimes it will light and run fine but then at the end when it’s on the cool-down running the fan on stop. I replaced the flame sensor for the first problem but that did not fix the problem
Probably a good idea to call a pro at this point as things get a little technical from this point forward. It is also a safety issue regarding a gas control. The only other advice I can offer you is to check to make sure it is getting the required voltage and that it is properly grounded.