Help with connecting Furnace Ignition Module...

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Old 12-23-17, 01:07 PM
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Help with connecting Furnace Ignition Module...

My original ignition module is Robertshaw SP735L Lennox. That one went out 10 months ago and the tech replaced it with a Robertshaw 780-715U. I'm having similar issues now, same as last time, the fan is blowing, so all else seems fine. So I'm guessing it's the module again. I’m thinking of ordering this Honeywell model: the Honeywell S8610U3009. In searching the reviews, someone said it replaced his SP735L. My thinking is that if the 780-715U replaced my SP735L, then this should work as well, correct? And if you’re wondering why don’t I just get the 780-715U again, it’s because it’s back-ordered by Amazon, while other sellers that are fulfilled by Amazon won’t ship to California. I only want to do fulfill by Amazon because I’m troubleshooting and if this isn’t the issue, then I can easily return with no hassle.

But I don't know anything about how the furnace and electrical wiring works so I'm stopped in my tracks cause the connections don't match up perfectly for me. Below are the pictures of the 780-715U and the Honeywell. Please see if I’m correct in my connections below, as well as help me fill in the missing gaps.

1. The Grey TH, mine is Brown TH would go to the Honeywell TH-W
2. The Blue PV, mine is Orange would go to the Honeywell PV
3. The White Sensor would go to the Honeywell Spark Sense? All the way to the right?
4. The MV red goes to the Honeywell MV
5. The White MV/PV, mine is Blue goes to Honeywell MV/PV
6. The Black TR, mine is Yellow goes where on the Honeywell?
7. The green ground is coming from a screw on the 780-715u and is connected to itself to the Green Ground. So I guess on the Honeywell, there will probably be a screw location for me to connect the green wire? But then where would I connect it, to the GND or the 24V(GND)?
8. The Orange Ignition goes where on the Honeywell?

Thank you for your time.
 
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  #2  
Old 12-23-17, 01:20 PM
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Your old board uses a flame sensor. The new one uses the spark electrode as a flame sensor. They MAY be compatible but no guarantee.

What is the problem you're having requiring board changes ?
This is not a normal occurrence.
 
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Old 12-23-17, 01:40 PM
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Seems to be the same symptoms. You hear it working, but it doesn't go to the final phase where you hear the full blown noise of it heating. In testing the fan blower, it works fine. Since changing the module fixed it last time, I'm thinking it's module again?

BTW, could my Nest be short circuiting it somehow? I noticed that I had the nest for about a year when the original module went out. When the tech came out, I removed the nest and reinstalled the original oldschool thermostat because I didn't want any confusion in case he wasn't familiar with it. Once he installed the module and left, I then re-installed my Nest. Ten months later... same issue. Could the Nest be the culprit?
 
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Old 12-23-17, 01:45 PM
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It may be the same exact problem as before but it's not the board. It's a dirty pilot or pilot orifice. If the pilot doesn't light and burn as a big bushy flame.... the main burner won;t light. Since it appears you have a flame sensor.... it may need to be cleaned.
 
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Old 12-23-17, 01:50 PM
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PJMax, so you're saying possibly that a year ago the tech cleaned it and switched the module when maybe I didn't need a new module? I still have that original SP715A, it would be interesting to see if it works after cleaning the pilot. Is this something we can DIY?
 
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Old 12-23-17, 03:32 PM
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Some modules are more sensitive to flame sensing.

You could try the other module but like I said it usually comes down to a pilot burner issue on those intermittent ignition systems.
 
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Old 12-23-17, 05:27 PM
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I don't know if this provides anymore clue, but right now, I don't even get a small flame or anything, it's nothing. You hear it working, but doesn't kick in. I make sure to wait for a bout 2 minutes, but still nothing.
 
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Old 12-23-17, 08:15 PM
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M,
If you go the sight below and type in you Honeywell ignition module in the search bar and then scroll down and click on installation instructions and scroll down to page 10 it will show you the compatible terminals for the new and old module.

http://www.supplyhouse.com/

Hope this helps a little.
 
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Old 12-23-17, 08:23 PM
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Thanks Spott! But before I go the module route, I think I'll try cleaning the pilot and sensor. The more I poke around, the more I understand the components. So I see that i have these parts:

1. The Pilot ignitor
2. And the Flame Sensor.



They are held in place by two flat head screws. Doesn't look too difficult to take out. PJMax, these are the items you suggest I clean, right?
 

Last edited by PJmax; 12-24-17 at 10:59 PM. Reason: removed unneeded pic
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Old 12-23-17, 09:25 PM
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What are important safety precautions before I poke around?

-Turn off power to furnace at breaker?
-Do I need to turn off gas at furnace? There seems to be two places I can turn it off. At the valve and at the knob, I labeled them A and B. Please look at the picture and advise which one I should turn off, or if I should turn off both.
 
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Old 12-23-17, 09:29 PM
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You can turn the gas off at A.

I added a picture to your post. That is a complete pilot and igniter assembly. If yours looks to be in bad shape it can be replaced. That assy does use a combination spark rod and flame sensor so that board you posted may work. The orifice that usually needs to be cleaned is a very tiny hole in that bottom tube where the deflector is. That assy is also held in place with the pilot gas tube which connects at the back of the pilot.
 
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Old 12-23-17, 10:20 PM
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PJ, what about the sensor? Leave it alone? I'm not seeing any initial flames or anything, so it's probably not the sensor, right? Because there is nothing to sense? Just clean the orifice in the pilot/ignitor assembly?
 
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Old 12-24-17, 01:37 PM
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Well, good news is I can take out the pilot ignitor and sensor and put it back with no issues. Bad news is that there doesn't seem to be a way to clean the orifice. I blast it with my air vacuum, but still nothing when I put it back, no light.

The orifice, I think is completely wedged inside. It's not the type that comes out with the tube. I saw a youtube video where a guy describes it as an intermittent pilot, and he says this model is meant to be replaced not repaired. I even held it in a vice for leverage and used a socket wrench to try and remove that main middle bolt, thinking I can then get to the orifice, but that thing won't budge. It's probably not a bolt. LOL! If I pull any harder, I think the whole assembly can get busted. I'll get the part from repairclinic since they have 365 days return policy.
 
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Old 12-24-17, 02:05 PM
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That may be a fixed orifice which means it may not be removable. If you can see the orifice hole you may be able to use a long thin piece of wire to clean it. You may also be able to go thru the gas line connection.
 
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Old 12-24-17, 02:33 PM
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I just took out the assembly again, don't know why I didn't take pictures last time. I can actually see light on the other side through the tiny hole. With flash, you can't see it in the picture, but would this mean it's pretty clean?
 
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Old 12-24-17, 03:51 PM
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If you can see thru it.... it's clear.

So what should happen is after that's back in. The spark ignition should start, the pilot valve should open and the pilot should light. There should be a good sized flame that the spark igniter needs to be in the flame.
 
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Old 12-24-17, 04:42 PM
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PJ, there is not even an initial flame. I hear it running, but no flame. Regardless of cleaning, is it common for a pilot assembly to simply go bad even if it's clean?

I guess I can order both a new pilot assembly and a new module just in case.
 
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Old 12-24-17, 04:47 PM
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Do you hear the spark ignition trying to spark at the pilot ?
If you have a meter check for 24vac from Pv to Pv/Mv terminal to make sure gas valve is getting power.
 
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Old 12-24-17, 05:28 PM
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What should it sound like, some sort of clicking? Here's a video with audio...
 
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Old 12-24-17, 07:09 PM
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M,
This is just a thought after seeing your video and following comments you made.

You said your pilot assembly is clear yet no gas is coming through.

If you stop and think for a minute if the pilot valve terminal on the module is allowing gas to go through the pilot tube and your assembly is unobstructed then the gas has to be coming out the orifice. It may not be lighting but it's coming out.

From your video it looks like you can see the pilot assembly with the ignition.

Can you see any kind of spark from the electrode. If there is no spark then there obviously cannot be any ignition.

It's only a small spark but even if you turn off the lights and run the furnace you should see something.

Your module is in the open. Did you try taking the wire off the terminal and with a screwdriver touching the terminal and pulling away a little to see if there is a spark. If you do this you can shut your main gas off while testing.

You may be getting gas but no spark or if everything is working your electrode could be worn or misaligned to not be able to spark, or maybe a cracked porcelain that is stopping the spark from reaching the metal.

Just a thought.
 
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Old 12-24-17, 08:09 PM
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Here's another thought after viewing that video. I didn't realize that was a draft induced furnace. If there is a vacuum/pressure switch problem there will not be ignition.

Check from ground (green wire) to Th (24v) on the ignition module. If you don't get any voltage..... there is another problem.

I may need the model number for that furnace.
 
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Old 12-24-17, 08:10 PM
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Thanks Spott! Which part is the electrode? The other rod? If you look at my pilot assembly picture. The outer rod is the flame senser, so the electrode is the other rod? Despite my interest to DIY everything, I actually lack common sense when it comes to gas and electrical stuff. I don't know the lingo.

BTW guys, Merry Christmas! It's funny, we have a Christmas Story on and I've been fiddling with the furnace all day. LOL!
 
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Old 12-24-17, 08:13 PM
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PJ, it's G16Q5X-100-7.

The inducer has a fan, right? It's spinning for what it's worth.
 
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Old 12-24-17, 08:19 PM
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The inducer is a blower that pushes out the exhaust gases. I can hear it running, The ignition module needs to know also that it is running. I'll check the wiring diagram.
 
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Old 12-24-17, 08:20 PM
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The electrode is the curved metal. the flame sensor is the straight. In order to get a spark to light the gas you must have 2 pieces of metal close enough to attract each other to create a spark.

I thought your orange wire was connected to it but looking at pics the orange wire looks like it's connected to the flame rod. What wire goes to your electrode.



Just got done watching It's a wonderful life myself. Try to never miss it.

Merry Christmas!!
 
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Old 12-24-17, 08:38 PM
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This furnace uses a separate flame sensor. This is the old system. That replacement pilot assembly that you and I previously posted uses the spark rod as a flame sensor.

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The link below is an excellent but old manual. Great diagnostics. You do need to check the voltage to the ignition board like I previously posted. The 24v to that module comes from the pressure switch and a heat limit switch.

LennoxG16.pdf
 
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Old 12-24-17, 10:01 PM
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PJ, when you get a chance, please give me step by step what to do. I have this meter below. Like what do I touch, and with which color, the red or the black rod/lead? Leave the furnace plugged in? Don't assume I know anything or any lingo, I need hand holding. LOL!
 
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Old 12-24-17, 10:57 PM
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Set the meter to AC V (about the 2 o'clock position). Since you're measuring AC voltage... there is no polarity to the leads. Touch one to a metal ground and the other to the terminal.

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Old 12-25-17, 11:46 AM
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PJ, not sure if I'm doing this correctly... I put one lead on the bolt of the ground and one on the first terminal the 24 vac TH. I got 25.5. I labeled the picture A and B. I also wasn't sure if I was simply suppose to do it while it's plugged in, but not calling for heat? But I wasn't getting any read, so I figured you meant to turn on the furnace and do it. So I turned on the furnace and that's when I was getting about 25.4 or 25.5. Let me know if I did that correctly.
 
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Old 12-25-17, 12:54 PM
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Yes... there is only 24vac present where you tested with a call for heat. If you have the 24vac that would mean that the pressure switch has proven and the heat limit switch is normal. At this point the spark ignition should start. You should hear a tick-tick-tick sound and like Spott mentioned.... look at the spark rod with no lights on.

If you don't see any spark..... the module is defective.
 
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Old 12-25-17, 01:27 PM
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Completely dark. Not spark, not a glimmer.

So it's the module?
 
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Old 12-25-17, 02:09 PM
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You've confirmed power on the module.... there is nothing left to check.

Did you try removing the spark wire from the module and try holding a screwdriver from ground to close that terminal. That would eliminate the spark wire and the spark electrode from being shorted.
 
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Old 12-25-17, 04:30 PM
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I didn't try the screwdriver thing, sounds uncomfortable to do. LOL! What should I do exactly? While the furnace is on trying to call for heat, I should put a screwdriver where? Spott says to take the "wire off the terminal." Which wire, the orange ignition? Or the 24 vac TH?

Lastly, I'm sorry for being slow, but like I said, I lack common sense in these things so I'm not completely understanding. By confirming power to the module, we've confirmed that it's defective?
 
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Old 12-25-17, 05:21 PM
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The orange wire. That is a high voltage terminal. Hold the plastic handle of the screwdriver.
 
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Old 12-25-17, 06:15 PM
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Okay PJ, in re-reading what we've been through, I think I'm getting it. Please confirm or correct these 3 assumptions to help me understand:

1. When you had me test for 24v at the TH terminal, you were making sure that the vacuum/pressure switch isn't the problem. Since the module gets the voltage from them, and since I got 25.5, that eliminates the vacuum/pressure switch as the culprit. Correct in my thinking?

2. Now as for the screw driving test. Are we trying to eliminate the pilot assembly as the culprit? If I get a spark at the ignition orange terminal, that means the pilot assembly is the culprit, correct?

3. If I get no spark doing the screwdriver test, that means the module is the culprit, correct?
 
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Old 12-25-17, 06:44 PM
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1 - correct.
2 - correct. The spark rod could be shorted.
3 - correct.
 
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Old 12-25-17, 07:00 PM
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Awesome!

Okay, one last thing before I do this. I will turn on the furnace, but I should shut off the main gas labeled A?
 
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Old 12-25-17, 07:03 PM
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Yes. You can turn the gas off.
 
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Old 12-25-17, 07:53 PM
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Okay PJ, I touched the orange ignition terminal with several screw drivers just in case. None of them gave a spark. Safe bet the module is the culprit?
 
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Old 12-25-17, 08:04 PM
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You need to disconnect that wire from the board. Use a screwdriver held close to that terminal and the green terminal above it to check for spark.
 
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