Kenmore furnace clank

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Old 02-02-18, 07:35 PM
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Kenmore furnace clank

Posted a video here on YouTube:
https://youtu.be/L_3wUpPB4P0

Kenmore high efficiency, 15-year old, multi-stage AC/DC furnace. Intermittent clank. Does not occur on every cycle, though it has the past two. It developed near the end of the cycle, as it is powering done. Is it dangerous? I obviously need some service, but would like to have an idea of what it is before calling, especially since it's so intermittent.

Video shows me touching the intake. I can feel the clank, though putting my ear to the outside wall, it sounds like it's inside the furnace.

The furnace is otherwise functioning normally. Hope I don't have to shut down. Very cold night here (20C/-4F, with colder windchills).
 

Last edited by silog1; 02-02-18 at 07:37 PM. Reason: Spelling
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Old 02-03-18, 05:22 AM
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Well, lots of views but no answers? I don't know much about furnaces (maybe obviously), but is it safe to remove the access cover with the furnace in the off position and then turn it back on to help me locate the precise problem. After taking this video, there we no further clanks the entire night. (I would suspect normal expansion contraction, but this is a new sound and very loud and around the gas intake pipe).
 
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Old 02-03-18, 09:10 AM
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Since the recording level on a camera is automatic it hard to localize a noise via camera. It sounds like something caught in the blower although the repetitive speed of the noise sounds to slow. My secondary thought is the gas valve but the control board won't usually let if go on that long.

You can slide the upper cover off to check the main burner section. The bottom cover also lifts up and off and has a safety switch that needs to be held in to operate the furnace with the lower cover off. You have a cat. Don't leave the furnace covers off unattended.

When it was making that noise.... was the main burner actually lit ?
 
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Old 02-03-18, 12:28 PM
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Thanks for that reply. At least I'm learning a thing or two about furnaces. So, I removed the top panel. Watching it cycle through everything, it looks like the noise was happening with the blower on, burner off.

It's not finished yet, but the noise occurs so infrequently, it's doubtful I'll capture it now. So far, it went through these steps:
1. Fan on
2. Pilot on
3. Pilot off, fan on
4. Pilot back on, eventually all burners on. All burners blowing blue.
5. Pilot and burners off, fan on
6. Blower on.
7. Off again.
8. #5 again, presumably same steps but longer this time to reach the desired temp.
The slow production is not much different than how it's always functioned from a cold start. It's not quick about heating the house the first time, but once it's going, it's been great. It does has some quirks, though. Sometimes it will just shut down quietly when reaching the temp (actually, it just did), other times it will give a short final fast burst (the blower?) and then shut down -- this tends to occur in colder conditions.
 

Last edited by silog1; 02-03-18 at 12:33 PM. Reason: added stuff, spelling
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Old 02-03-18, 01:07 PM
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There is a very distinct pattern and timing to the process.
1) call for heat and draft inducer blower starts.
2) approx 15 seconds of pre-purge
3) spark igniter starts and pilot lights.
4) spark igniter stops.
5) main burner lights.
6) main blower starts.

Where is the problem happening ?
So far.... it sounds to me like the pilot assembly needs servicing.
 
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Old 02-03-18, 01:49 PM
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The noise always occurs near the end of a cycle, apparently when just the blower is on the lights are off; I will attempt to confirm this the next time I hear it.

Are you thinking that the pilot is shutting down prematurely, but could that cause that type of noise?

Even when new, this furnace always went through the stages slowly. As I recall, we were told that because of it's AC/DC multi-stage way of using energy, it wouldn't work quite the same way. At the time, the furnace was on the expensive end -- top of their line.

I agree it probably needs servicing, but I'd just like to make sure the clank gets addressed. By "service," I think you mean repair, not maintenance.
 
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Old 02-03-18, 02:14 PM
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I'm trying to assess what is clanking. If the pilot is igniting and then the burner runs ok.... that is probably not the issue. That leaves something in the main blower.
 
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Old 02-03-18, 03:09 PM
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Yeah, really appreciate your help. I will let you know if I'm able to see it with the clank going. In any case, I will probably go ahead and get someone to look at it early next week.
 
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