View Full Version : Pilot ignites but won't lite

Nov 9, 2017, 07:09 AM
I have a gupi 100-4. The pilot assembly (igniter and flame sensor) are new. Pilot lite will ignore for 5 to 10 seconds and will then go out without the burners kiting. Have to shut it off and turn back on in order for it to cycle again.

Nov 9, 2017, 09:43 AM
Please turn up the temperature of your home thermostat, and describe what happens. It may take a minute to kick in but you should hear other components like the blower fan clicking to start. Let us know please.

I looked around and found this very interesting post for you to read for some insights into trouble shooting and diagnosing your furnace.


Well, after replacing the air pressure switch, spark ignitor, ignition module, and control board, I STILL had the same problem. It ended up being the high-limit switch! I've learned a valuable lesson here though, start with the LEAST expensive items first. After spending 2 days and $375.00 it ended up being an inexpensive part and easy to replace! Going into this project, I knew nothing about furnaces, now I know every part and it's functions so, at least I gained something out of this horrific job! I just hope this post helps someone else out somewhere down the line, along with their money and time!

The moral is just changing parts is expensive, and maybe better to invest in an ohmmeter and learning the proper way to use it.

Nov 9, 2017, 12:28 PM
Thermostat is at 70, house is 62. The flute fan turns on, pilot lites, stays on for 5 to 10 seconds and goes out. The flute fan remains running until I shut the switch off. Does not try to reignite unless shut off and turned back on. Does this furnace have a high limit switch?

Nov 9, 2017, 12:46 PM
All furnace do. Your components need to be checked for continuity to confirm function.

Nov 9, 2017, 04:35 PM
I checked the high limit switch, it is good, I also check air pressure switch, what else should I check?

Nov 9, 2017, 06:58 PM

Goodman - Gray Furnaceman Furnace Troubleshoot and Repair (http://www.grayfurnaceman.com/-goodman.html)


Nov 9, 2017, 07:16 PM
I am.getting 24 volts to the pilot valve and getting 0 to the main valve, what could be the cause of this?

Nov 10, 2017, 07:47 AM

Many Goodman domestic furnaces installed from the 1980s to the present time are the 80 percent efficient Janitrol Type GMP Models. These include model numbers 050, 075, 100 and 125. When the furnace stops working, a trouble code LED is visible through a small round sight glass mounted on the blower access door. The number of flashes allows you to interpret the codes to give you an idea of the maintenance required.

If you have them please convey what faults they indicate. Forgive me for not asking about the error codes earlier, but this is generally the first step in the process, and may confirm you have a bad valve.

Please VERIFY.

Nov 10, 2017, 08:54 AM
Mine does not have the light... I was hoping it did.

Nov 10, 2017, 10:15 AM
Then we proceed to the NEXT step in the process,

Pilot gas furnace, no heat, gas valve not opening - Gray Furnaceman Furnace Troubleshoot and Repair (http://www.grayfurnaceman.com/fag-wpilot-no-power-to-gas-valve.html)

If you find a limit or fusible link failed, it should not be bypassed. These are safety controls and bypassing them could easily cause a fire in the structure.
A replacement control should be purchased.

Nov 11, 2017, 05:14 PM
All sensors and limit switches check out, not getting 24 volts for the main valve from the ignition module. Does the signal come from the ignition module or circuit board?

Nov 11, 2017, 07:55 PM
Your components are all linked together in series You will have to trace all your wires from the valve to mother board which probably includes a capacitor or two, and maybe a few fusible links to the blower and PRESSURE SWITCH . That's why I included the grayfurnaceman link. I could be wrong since you said you have a new flame sensor lets just double check that wiring to the gas valve just to eliminate the obvious. If all that checks out good, then its just the valve left right?

Did you review those videos I gave you? They are pretty good at laying out the trouble shooting process (mostly tracing and checking wires and components). A few you will have to jumper and test, including your home thermostat.

https://www.bing.com/videos/search?q=pilot+ignites+but+won%27t+lite+on+gupi+10 0-4+furnace&qpvt=pilot+ignites+but+won%27t+lite+on+gupi+100-4+furnace&view=detail&mid=CA5576D0EB2020C2C0E7CA5576D0EB2020C2C0E7&FORM=VRDGAR

Everything that needs checking is in https://www.askmehelpdesk.com/heating-air-conditioning/goodman-gupi100-4-will-not-ignite-205334.html post 8 and 10 (PDF)

This is also a helpful site


Tedious I know that's why techs get paid the big buck and have to spend hours learning this stuff.

Nov 14, 2017, 06:29 PM
I am getting 24 volts through the pressure switch, high limit switch and roll out sensor. I put in a new control board and a new flame sensor. However I can not get a microamp reading off the new or old sensor. Not sure if I am doing something wrong there or what. Is it possible that the igniter module is bad or the new flame sensor is bad as well? Igniter only sparks for 5 seconds and goes out and does not retry unless shut off and turned back on.

Nov 15, 2017, 06:15 AM
From repair clinic site;

The draft inducer motor draws air into the heat exchanger and then exhausts it out the flue. The pressure switch senses a pressure change and closes a switch to signal the control board that the furnace has proper air flow. If the draft inducer motor is defective, it may be unable to close the pressure switch, causing the ignition process to stall and the furnace to shut off after a few minutes. If the ignition process stalls, the furnace will shut off. If the draft inducer motor is at fault, replace it.

Always check for air flow and ventilation. Specifically inspect flue for blockages even if these components have power.

Nov 15, 2017, 07:22 AM
I will check the chimney tonight, the pressure switch has continuity after the flute fan turns on... so that means it is clear and drawing air in and closing the switch right?

Nov 15, 2017, 09:06 AM

Lets look at that gas valve.


Nov 15, 2017, 09:50 AM
If I run a jumper from the pilot valve to the main valve. Both the main burners and the pilot will lite but only for the 5 seconds.

Nov 15, 2017, 10:15 AM
This is going to sound stupid but it almost always works for me... after a furnace has been off for awhile it seems that the pressure switch gets "sticky". I pull off the tube from the intake where it connects to the area near the combustion fan and blow and suck a few times to "unstick" it. I've been able to restart hundreds of furnaces with "sticky" valves that way. I am not a HVAC tech or an expert in anything really (except customer relations, maybe) but I have built a pretty good handyman business. Prayer doesn't hurt either. God Luck!

Nov 15, 2017, 12:33 PM
Willing to try anything at this point... thank you for the advise.

Nov 15, 2017, 01:15 PM
A clogged tube between PS and inducer motor is a possibility. Here are a series of videos to make sure you checked the whole thing properly.

https://www.bing.com/videos/search?q=gupi+100+4+main+burners+and+the+pilot+wil l+lite+but+only+for+the+5+seconds.+&&view=detail&mid=C74A05D353BA76642259C74A05D353BA76642259&rvsmid=28ED07BD06F2FAEB89BD28ED07BD06F2FAEB89BD&FORM=VDMCNR

I will check the chimney tonight, the pressure switch has continuity after the flute fan turns on... so that means it is clear and drawing air in and closing the switch right?

Not necessarily. Continuity and function must be verified. Your induction motor flue doesn't go to the chimney, but to a vent pipe on the roof. Its hard to follow your process, but if jumpering the valve produces flame then your inducer motor, pressure sensor, is suspect, not the valve. But I await your latest testing results.

When you check the PS tube, check the fittings also to the induction motor. Should have pointed that out when I told you to check the pressure switch.

Nov 15, 2017, 05:17 PM
Tube off the pressure switch is clear, I blew into the pressure switch and into the fan housing. Made sure the vent was clear as well. Still only lite the pilot for 5 seconds and didn't not try to ignite again.

Nov 16, 2017, 03:46 AM
I think you're at a point you either have to review your process and procedures, and see if you have missed something, or get fresh eyes on the problem. At this point I recommend both. Learning is a difficult enough of a process in of itself, and learning about a furnace takes many hours of instruction even for those with skills.

Please keep us updated on your progress. Good Luck. Sorry I was of no help.

Nov 22, 2017, 03:49 PM
Well, I order an igniter module and put in... turns out that was the problem furnace is now running. Thank you for all of your help

Nov 22, 2017, 04:54 PM
Boy am I glad you got it. Please if you have time, explain how you arrived at the igniter module as the problem?

Dec 8, 2017, 04:24 PM
Well I checked all the sensors, then it occurred to me that the furnace would only try to cycle once and it was supposed to try every 90 seconds for 5 minutes, so I took a stab in the dark and turns out that I got lucky... still going good!

Dec 8, 2017, 04:55 PM
Thanks for getting back to us. LOL, I rather be lucky than good myself. 8D! I thought we checked that ignition module with the gas valve. Oh well, we can till celebrate with your savings.