Gas Furnace Ignitor Problem

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  #1  
Old 09-25-18, 05:25 PM
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Gas Furnace Ignitor Problem

My York/Luxaire gas furnace PCMU-L016N095B does not fire up. The problem seems to be that the "hot surface ignitor" is not getting powered up. I checked it for conductivity and got around 120 Ohms on it when cold. Unplugging the ignitor and attaching the multi-meter I can't detect any voltage during the call for heat cycle.

Upon initiating the call for heat cycle, the blower runs first, then after a while I can hear the gas flowing, but the ignitor does not start to glow and the gas shuts down. However at this point if I light the flames by hand with a lighter torch I can get the furnace to heat for a while.
Is this a case of a broken circuit board or is there another step that could prevent the ignitor from getting powered up?

What could be the problem? Is there anything additional I could test?

Thanks

ps. The ignitor was already replaced one time 3 years ago by a hvac repairman. Its a flat 271N 02532625 type.
 
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Old 09-25-18, 05:28 PM
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Welcome to the forums.

That model number looks very close to my furnace. If the igniter continuity is good and there is no voltage when it should be heating.... the relay on the control board has failed and the board will need replacement.
 
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Old 09-25-18, 06:19 PM
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Thanks for your answer Pete. The control board seems to be located inside some metal box within the blower chamber, which I haven't yet dared to open up. Replacing the board sounds like its not going to be cheap ...
 
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Old 09-25-18, 06:24 PM
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Nah..... that board is not expensive. I believe it's a White-Rodgers ignition board.
Something is not quite right with your model number.

Yes.... it's in that metal box that hangs in the blower area.
 
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Old 09-26-18, 11:16 AM
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Correct, opened up the box and it revealed a White Rodgers 50E47-070 controller. This model seems to be difficult to find, however there is a generic unit 50E47-843 that is supposed to replace older models.

The controller has a control light for error status, however unfortunately its not possible to see during operation since its all inside the metal box. In addition the lower furnace cabinet need to be closed and push against a door safety switch in order for the furnace to be able to power up.
 

Last edited by dblko; 09-26-18 at 12:13 PM.
  #6  
Old 09-26-18, 01:07 PM
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db,
Just a thought. Those ignitors are very delicate. It may have a hair line crack which will stop it from igniting. You may want to look at it closely.

Do not touch ignitor with hands. The oil from your skin could effect the ignitor.

Hope this helps a little.
 
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Old 09-26-18, 05:01 PM
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Thanks Spott, I have a replacement ignitor on order and will try it when I get it. Hope this will fix it, but considering that the old one actually had conductivity and I could not detect any voltage during the ignition cycle it might not work. Would be great if its an easy fix. Might have to go the controller route, not sure if I should try to replace it myself. However getting a professional service is very costly in my area, I believe I would be looking at almost $1000. Going the DIY way, the controller unit goes for about $100 online.
 
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Old 09-26-18, 05:24 PM
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I've replaced both a hot surface ignitor and a control board, and neither is a tough chore.

As Spott said, I'm wondering if your HSI is defective. It's the easier, cheaper solution, and if it turns out to not solve the problem you'll have a replacement part in the inventory, ready to install on a cold morning when the HSI finally does go.

If it turns out to be the board you can shop for price and quick shipping on the web. Take a photo of the old board and where/how the connectors attach, and compare the new board to the old. You may be able to disconnect a part from the old and attach it directly to the new, then mount the board. At first it's intimidating, because it's a furnace and gas and electricity, but if you break the process down into small tasks it's actually very easy. Let us know how it goes!
 
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Old 09-26-18, 07:26 PM
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Yes.... those flat igniters crack very easily but if you don't get the 120vAC to the plug when it should be heating..... it's the board.

York OEM # 025-25436 (50e47-70) which is currently replaced by the 50E47-843 controller.
You can run the furnace with the silver box open for testing purposes..... just hold the door safety switch in.

That control board runs on 24vAC so the two igniter terminals... are just a switch. The way I test this system is to put my voltmeter set to 120vAC mode on the L1 and IGN terminals where the wires go into the plug. Hold the safety button in and you should measure 120vAC. When the igniter should be heating...... you should measure 0v. If it stays at 120vAC..... the board is not working correctly. If you don't measure 120vAC on those two terminals from the start..... it is not a board problem.

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Old 09-26-18, 08:41 PM
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Thanks Pete. That's interesting.
I don't quite get your first statement saying the board puts out 24v only since its just a switch. The labeling seems to say its supposed to put out 120v on the ignitor?

For the testing, are you are saying the IGN - L1 terminals at the controller work kind of in reverse, putting out 120vAC when the ignitor is supposed to be off, and 0v when the ignitor is on ?

ps.
Actually, is it that L1 is always hot on 120v? So while IGN is initially at 0v, we can measure a 120v drop between those two. When ING goes hot to power the ignitor it goes to 120v and we measure a 0v drop between L1 and IGN. Right?
 
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Old 09-26-18, 09:26 PM
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The L1 and IGN are just terminals that connect to a relay inside the module. The board runs on 24vAC. It doesn't supply anything to those two terminals. When the board says "igniter heat" there is a direct short between the L1 and IGN (HSI) terminals.

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Old 09-27-18, 04:18 AM
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OK, thanks for clarifying and posting the diagram.

This would mean that doing the voltage measurements you mentioned above would need to be done while the terminals are still connected to the L1-HSI connector? In my case there's a plug that covers both terminals that doesn't seem to have any exposed metal parts where I could easily attach the leads of the meters.

Alternatively, what about unplugging the L1-HSI connector and try to use the multi-meter to read connectivity on those terminals, assuming its just a relay without any power source behind it? However that sounds somewhat more risky to use the meter in this mode on a live circuit?
 
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Old 09-30-18, 07:51 AM
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ignitor plug doesn't fit

The replacement ignitor that I had ordered arrived, but strangely its plug does not fit into the old connector. The ignitor plug on the ignitor iteself has the correct shape, however the pins inside are not rounded but hollow. They clash with the pins on the furnace side. Instead I was expecting rounded pins, just like the L1-HC pins on the control board picture. I looks like the irnitor side plug has female pins instead of male pins. Is there a convention for this? How can this happen, so strange?
 
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Last edited by dblko; 09-30-18 at 08:56 AM.
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Old 09-30-18, 02:22 PM
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To clarify below are pictures of the connectors from the old ignitor, which have opposite pins from the one I ordered:
 
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Old 09-30-18, 03:36 PM
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Cut the plugs off and use wire nuts.
 
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Old 10-15-18, 12:00 PM
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As a test I unplugged the L1-HSI plug connector from he control board and bridged it on the cable side with a piece of wire, in order to directly connect the hot L1 to HSI. Running the furnace this way, the ignitor starts glowing after powering the furnace up. This shows that the ignitor itself and the wiring is OK. Does this mean the control board is dead for sure, or could there be something else that prevent the L1-HSI relay from making a connection? The furnace will try to ignite three times, afterwards the control board control lamp flashes red. Again, the furnace also works if I manually light the gas with the piece of glowing wood.
 
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Old 10-18-18, 02:19 PM
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Quick update, I finally got the new 50E47-843 control board for $90 from Amazon. Easy install, even the included adapter for the L-IGN connector did fit. It works perfectly now. Saved me allot of money. As comparison, last time a local HVAC company had charged me $800 for replacing the furnace gas valve that also goes for $90 online.

ps.
The new control comes with keys to set a specific combination of timings. The manual https://images-na.ssl-images-amazon....1k-9hQovJL.pdf recommends the "A" key for my old model which sets retries to 0, however the old controls used 2 retries which would appear the "B" key should be the better fit with all other settings the same. Probably it does not matter much as long it works, I used the recommended "A" key for now, still strange.
 

Last edited by dblko; 10-18-18 at 03:29 PM.
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Old 10-18-18, 09:24 PM
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Look on your old control. The specs should be listed. The key should match those specs.
 
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Old 10-19-18, 04:29 AM
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Good on ya! Congrats on your repair work!
 
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Old 10-19-18, 06:00 AM
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Thanks for all the help, could not have gotten so far without the forum.
 
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