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llmercll 10-13-2012 07:08 PM

Gas Heater Ignitor won't "glow"

I have a gas central air heater/AC that is acting up. We turned on the heat the other day but it wouldn't light =/

Every year I have to clean the flame sensor and all is well, unfortunately the ignitor isn't even glowing this time.

I figure I may have a cracked ignitor, and want to take a multimeter to it to confirm, but am not sure exactly "where" to test. Would I just put it on the positive and negative cables coming from the computer?


biggles 10-13-2012 07:23 PM

set the meter to read OHMs with the power off and the wires from the ignitor off the control module should read a dead short or resistance if the meter sits at 00.0 the coil is broken/craked.then with the wires off the board call heat and read the terminals you pulled the wires off to read the voltage make sure the board is sending a call.

llmercll 10-13-2012 08:06 PM

Thanks for the reply,

I pulled the ignitor and sure enough it has a crack, also showing "infinite" resistance when I check ohms

I'd like to make sure my wires are working properly before ordering my replacement ignitor and calling it a day though, Should I just turn the heater on and check the voltage of the two wires that go into the ignitor? (sounds dangerous)


how 10-14-2012 01:36 AM

Just make sure that the Hot surface Igniter is unpluged and you are just testing the wires supplying it with power. The point is to do it in such a way that those live feed wire ends have no way of contacting each other or any electrically conductive surface. Also make sure that your meter probe ends don't cross and connect with each other during your measurement test.

Tell us the make and model of your furnace. Not all furnaces have igniters operating on 120V.

If that igniter is cracked, you already have your reason why it's not working.

llmercll 10-17-2012 03:50 PM

Thanks everyone, replacing the ignitor did the trick =)

llmercll 11-03-2012 07:29 AM

Ahh not even two weeks and the new ignitor has a crack in it =/

I've got a replacement on the way. Any ideas why it burned out so quickly? I definitely did not touch the ceramic part.


beenthere 11-03-2012 07:53 AM

Did you put a 24 volt HSI on a 120 volt system.

yuri 11-03-2012 02:13 PM

need to know the model and age of furnace. post a pic of the burners. not all igniters use 120 volts and low voltage can burn them out.

llmercll 11-06-2012 07:33 AM

Sorry for the late reply, and thank you for the comments.

I believe I am using the right voltage. The unit I replaced had the same model number as one that's been in there a few years.

Here are some pictures I took

It looks like the furnace is a GMP and is about 20 years old.

I didn't notice any polarity markings on the HSI, is it possible I may have wired it wrong? Other than that I'm thinking maybe the area around it was dirty and some dirt got on the ceramic, or possibly it was just defective?

I've got my replacement coming today and don't want to mess up, it's been really cold here in NY =p


Marty S. 11-06-2012 01:07 PM

20 year old gmp is pretty much guaranteed to have a cracked heat exchanger. Rough ignitions will crack those fragile ignitors quickly.

llmercll 11-06-2012 04:56 PM

Got the new HSI, installed it with no troubles, furnace is working now. But for how long =/

How can I check if I have a cracked heat exchanger?


beenthere 11-06-2012 05:09 PM

One way is to watch the flames when it first starts, and keep watching them till the blower starts. Do they start jumping around. if so, good chance the heat exchanger is cracked.

ben's plumbing 11-06-2012 05:18 PM


Originally Posted by llmercll (Post 1046136)
Got the new HSI, installed it with no troubles, furnace is working now. But for how long =/

How can I check if I have a cracked heat exchanger?


as b t said watch flames after blower starts....but we use a camera..may still want to have a pro check it to be double safe...ben sr

Marty S. 11-06-2012 05:24 PM

Remove the blower and crawl up in there with a bright flashlight. Often times on those there will be rings sitting on top of the blower assembly. They are what's supposed to hold the heat exchanger together so finding one means the heat exchanger is shot and there will be no need to crawl in.

llmercll 11-06-2012 05:38 PM

Thanks a lot for the input. Fortunately the flame stays the same when burner starts, maybe it's a bit more "orange" but it's extremely subtle if anything. I'm also taking my CO detector around because now I'm worried haha. Everything seems good there though.

After reading this thread I did notice my furnace cycles quite a bit. It will come on for maybe 3 minutes, go off for 5, and repeat. I thought that was normal but I'm not so sure now. If the temp drops to 69 it will turn on until it hits 70. In the summertime my HVAC guy told me the AC's evaporator coil was clogged, causing my Freon pipes to freeze. He cleaned it up and it worked great after that, but could it be related?

I cant have this thing failing every 2 weeks =/


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