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johnmeyer  
#1 Posted : Saturday, May 10, 2014 8:24:30 AM(UTC)
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johnmeyer

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Joined: 7/28/2010(UTC)
Posts: 17

Problem: On my Thermador white glass top GGSCV365W cooktop, the rear XLO burner turns on and I can adjust the flame just like I always have. However, after about two minutes, the flame goes out, and the igniter continuously sparks. All other burners are unaffected and operate normally.

Here is a picture of the cooktop:

UserPostedImage

Question #1: Is this problem likely caused by a defective solenoid, or is something else more likely the cause?

Question #2: How to I remove this cooktop for service? Other posts in this forum describe removing the screws under the burner cap, but my cooktop does not have those screws (see picture below). Instead, it only has a brass nut in the center. Here is what that looks like:

UserPostedImage

Thanks in advance for any help you can provide.

John
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johnmeyer  
#2 Posted : Sunday, May 25, 2014 2:05:09 PM(UTC)
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johnmeyer

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OK, I found posts elsewhere which describe how to disassemble the cooktop. However, I haven't yet gotten any guidance on which part is the likely cause of the problem.

It sure seems to me like the problem must be something that is very near the burner and is therefore being affected by heat. I say this because the burner operates perfectly normally at first: it starts normally; I can adjust the flame up and down with no problem; and the sparking from the ignitor stops as soon as the flame catches. But, about 1-2 minutes after the burner is running, the flame goes out and the ignitor starts sparking repeatedly.

Therefore, it seems to me that heat from the burner must be causing a disruption in the flame-sensing mechanism.

This has to be happening somewhere near the burner, because the problem happens even when this is the only burner in use. It never happens until the burner has gotten good and hot, and it seems to happen more quickly when there is a large pot or pan covering the burner than when a small pan is used.

Once again, any help or advice would be much appreciated.
Therm Owner  
#3 Posted : Wednesday, June 25, 2014 8:49:43 AM(UTC)
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Therm Owner

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Just thought I would suggest something as I own a pro line Thermador gas range with 2 xtra-low top burners. once you turn the dial past the simmer setting you get a timed simmer setting which turns the flame on and off for varying amounts of time depending on how low you set it. It is computer controlled and is supposed to turn on and off to get the temperatures lower than the lowest simmer setting. Hope this helps. even though you don't have the same model this may also be how your burner works. wait to see if the burner relights after x number of minutes on its own in the extra low setting range.


johnmeyer  
#4 Posted : Wednesday, June 25, 2014 10:16:29 AM(UTC)
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johnmeyer

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Originally Posted by: Therm Owner Go to Quoted Post
Once you turn the dial past the simmer setting you get a timed simmer setting which turns the flame on and off for varying amounts of time depending on how low you set it. It is computer controlled and is supposed to turn on and off to get the temperatures lower than the lowest simmer setting ... wait to see if the burner relights after x number of minutes on its own in the extra low setting range.

Thanks for the reply. You give a very accurate description of how my two XLO burners work. However, this problem happens when the burner is turned up to one of the high settings, which doesn't result in any on/off cycling.

It seems clear to me that there is some connection or component that is in close proximity to heat, and which therefore opens up after it gets hot.

Hmmm .... writing that gave me an idea ...

I just turned on the problem burner (left rear XLO) but did NOT put a pan above it. I set the burner to Hi (i.e., full on). I then set a timer, both to make certain I remembered to turn it off, and also to see if it turned itself off and then started continuously sparking (which is the failure mode). With a pan over the flame, the problem happens in about two minutes.

Waiting ...

Well, that was useful. The burner did NOT turn off and did not start sparking, even after over five minutes. Since it has been failing 100% of the time, for the past six months, but always with a pan over the burner, and always in less than two minutes, I think I have determined that the problem is with a connection or component that is underneath or within the proximity of the burner cover.

This makes me think it is nothing other than a connection that needs to be re-crimped.

Does anyone else have an idea or suggestions? What is directly underneath the cover? I'd feel more comfortable tackling the job if I had a little insight from someone that has worked on this before.

Thanks!
johnmeyer  
#5 Posted : Thursday, July 10, 2014 2:54:56 PM(UTC)
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johnmeyer

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[edit]I thought I solved the problem, but it returned. I am now going to replace the ignitor. The following is what I did. This initially seemed to fix the problem, but it later returned. I assume that the ignitor assembly also is responsible for sensing whether there is still a flame.



I turned off the gas and electricity. I then took off the burner plate. This is done by unscrewing the brass nut (burner orifice) in the center of the burner plate. Before I took off the nut, I marked its original location with a pencil mark so that when I reassembled it, I would get roughly the same degree of tightness.

Once opened, it became quite clear that the only two things that could cause the problem would be a faulty ignitor, or a bad connection to the ignitor (it is connected with a standard spade lug crimp connector). I say this because there simply isn't anything else anywhere nearby that could possibly be affected by the heat.

Since I hadn't purchased any parts, I pulled off the crimp connector and, while I was at it, I took out the ignitor. I cleaned the ignitor carefully, and blew it out with 90 psi compressed air. I then cleaned the ignitor contacts with a wire brush, and also scraped the inside of the crimp connector. Then, very carefully, with a small thin-nosed pliers, I bent the crimp connectors slightly in order to create a tighter connection. I then reconnected the spade lug to the ignitor and reassembled everything.

To test, I put the biggest pan I have onto the burner, and filled it with some water. I turned the burner to high. For the past year, this would cause the burner to start sparking within 1-2 minutes. This time, it was still going strong after seven minutes.

Solved!

Thanks to all for their help.
johnmeyer  
#6 Posted : Tuesday, July 15, 2014 6:40:06 PM(UTC)
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johnmeyer

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I ordered the ignitor from Appliance Parts Pro, and also ordered the gasket that goes under the inner burner ring. Unfortunately, this did not fix the problem.

I then did some more testing. I have already described the problem in my earlier posts. I found two interesting things in my new testing:

1. If I turn on the two adjacent burners (one of which is also an XLO burner), then after about five minutes, if I attempt to turn on the bad burner, it sparks, but the gas solenoid does not click on.

2. The two XLO burners have a very loud solenoid that clicks just prior to the ignition spark, and then click again when the gas is turned off, or when the burner is cycling on/off during the really low XLO setting. The other three burners only have a very soft solenoid sound when the gas comes on or is turned off.

So, it appears that there is some sort of self-heating going on inside of some part and that this causes the loud solenoid to shut off, and then no longer work until everything cools down.

I wish there were someone who has repaired these before that could give me a clue what to replace. My instinct tells me that the problem lies inside of whatever module is used to drive the loud solenoid. If it were the solenoid itself, then I wouldn't think I could cause it to fail by running the two adjacent burners, but not the one that is bad.

The spark is loud and bright, and the spark clicks about twice a second when it tries to light the bad burner when the gas is not being supplied (because the solenoid hasn't turned on the gas).

After about fifteen minutes, the burner will once again operate normally. It once again lights normally, and the flame adjusts normally, and the XLO works as it should, turning the flame on/off.

Any ideas??
fabelman  
#7 Posted : Wednesday, September 3, 2014 5:15:37 PM(UTC)
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fabelman

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Originally Posted by: johnmeyer Go to Quoted Post
I ordered the ignitor from Appliance Parts Pro, and also ordered the gasket that goes under the inner burner ring. Unfortunately, this did not fix the problem.

I then did some more testing. I have already described the problem in my earlier posts. I found two interesting things in my new testing:

1. If I turn on the two adjacent burners (one of which is also an XLO burner), then after about five minutes, if I attempt to turn on the bad burner, it sparks, but the gas solenoid does not click on.

2. The two XLO burners have a very loud solenoid that clicks just prior to the ignition spark, and then click again when the gas is turned off, or when the burner is cycling on/off during the really low XLO setting. The other three burners only have a very soft solenoid sound when the gas comes on or is turned off.

So, it appears that there is some sort of self-heating going on inside of some part and that this causes the loud solenoid to shut off, and then no longer work until everything cools down.

I wish there were someone who has repaired these before that could give me a clue what to replace. My instinct tells me that the problem lies inside of whatever module is used to drive the loud solenoid. If it were the solenoid itself, then I wouldn't think I could cause it to fail by running the two adjacent burners, but not the one that is bad.

The spark is loud and bright, and the spark clicks about twice a second when it tries to light the bad burner when the gas is not being supplied (because the solenoid hasn't turned on the gas).

After about fifteen minutes, the burner will once again operate normally. It once again lights normally, and the flame adjusts normally, and the XLO works as it should, turning the flame on/off.

Any ideas??

Did you ever resolve the problem? I have the same.
johnmeyer  
#8 Posted : Wednesday, September 3, 2014 5:59:17 PM(UTC)
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johnmeyer

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Originally Posted by: fabelman Go to Quoted Post
Did you ever resolve the problem? I have the same.
No, I have not, but at some point this fall I'll just have to pull the whole thing apart and take a closer look.

Since I first posted many months ago, I have occasionally been having the right rear burner start sparking (i.e., the same symptoms as the left rear XLO burner). This is NOT one of the XLO burners.

Looking at the schematic, all the ignitors terminate in the same black box. I wish someone could tell me if this box not only provides the spark, but also senses whether the ignitor is hot. It seems as though this sensing function has failed.

When I do finally tackle this, I will probably try to open up the black box and look inside. I'm an EE and do component level repair on most things. 90% of electronic problems are caused by electrolytic capacitors, so that is always the first thing to look at. Corroded terminals and cold solder joints are also quite likely. These three likely causes are made even more likely because so many people, here and elsewhere, have reported similar problems. Therefore it is likely a common manufacturing defect or bad part. A LOT of electronics manufactured in the early 1990s used defective electrolytic capacitors, and this cooktop was manufactured in 1994.

If and when I get it fixed, I'll report back. In the meantime, I purchased a very nice portable induction cooktop which gives me back the large SLO burner that is now out of service.
GeoEdwards  
#9 Posted : Sunday, March 8, 2015 12:44:42 PM(UTC)
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GeoEdwards

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I have the same issue on my Thermador PRG364GDUS. I am glad an electrical engineer is tackling it. It seems to me, if I have ignition and I do, and I have gas and I do, and it burns for a bit then arbitrarily turns off, it is probably in the circuitry controlling the valve.

It appears the on/off nature of the simmer burners are regulated by the potentiometer assembly which includes circuit boards that go in front of the two simmer valves that connect to a blue box that is directly behind the kick plate at the bottom of the range.

UserPostedImage
BOSCH POTENTIOMETER KIT 497235

If you figure it out, let me know. I love my stove and cook an awful lot.

George
johnmeyer  
#10 Posted : Sunday, March 8, 2015 3:01:32 PM(UTC)
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johnmeyer

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I have put this project on "the back burner," so to speak, because AppliancePartsPros, and the other sites, have been running out of various parts I might need. In particular, the porcelain on two of the burner plates has chipped, and I was hoping to replace those, while I had the entire thing apart. Also, I'll need new gaskets under each silver burner disc (the part that sits on top of the white burner plate. I found this out when I replaced the ignitor on the bad burner (which didn't fix the problem) and found out that the gasket was nothing but dust.

Since the other four burners still work, I've been reluctant to take something that is still 80% functioning, and potentially render it 100% inoperable.

A few months ago, we went shopping for a replacement cooktop, but we didn't like anything we saw, and we considered every brand, and didn't put any limit on price. This made us very reluctant to do anything that might damage this cooktop. I did purchase a portable induction cooktop, and that has been taking the place of the intermittent burner. I can still use our burner for 2-4 minutes before it shuts down, so I can sometimes get something started on the big burner and finish it on a smaller burner.

The other problem is that this unit has the integrated downdraft exhaust, and we had the fan mounted forty feet away, on an exterior wall, in order to reduce noise in the kitchen. Any new cooktop will also need a new fan arrangement, and that is going to be complicated.

I probably should just quit being such a wus, open the thing up, find the bad part, and be done with it.

I'll certainly post here if I succeed in actually fixing the thing.
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