FIXED Thermador SMW272YP - not heating, 100F on display

sevencube

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SMW272YP
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Hi. I'm hoping someone here smarter than myself can help me with my triple stack Thermador in-wall oven not heating. To preface, we've never done the self-cleaning and it was working fine since we moved in (over a year ago) and then all of the sudden the oven stopped heating at all and shows 100F on the display but the element isn't even starting to warm. The loud fan does kick on like it does when the oven is working properly but no heat at all and a constant 100F on the display. The techs and I have tried tricking it to heat by starting with broil cycle but that doesn't work either. Oven will not heat no matter what we try. We've had 5 or 6 techs come to look at it/"fix" it starting with home guard insurance (which was a nightmare) and we're still no closer to having our oven working again.

The first two techs came in a diagnosed as bad relay board and/or relay switch and Thermador no longer makes these parts. I'm pretty sure relay board = control board and relay switch = the bake & broil relays on the control board. After home guard wasted 2 months "waiting for parts", they decided to tell us that our oven is "commercial grade" and not covered by them (laugh out loud), they decided to pay us out maybe 1/5 the cost of a new oven.

At this point, I researched enough to take out the control board and display board and send to a circuit board repair company who tested and said the board is working fine, so they sent it back. I reinstalled and still same issue. So I called a local appliance repair company to come out. When they did I told them that the board has tested good at control board repair company, so he quickly diagnosed it as bad cut-off switch/button. This is a $5 part located in a small panel directly above the lower oven (only oven, not counting the microwave above it). He had my hopes up because he pressed that reset button for 2 seconds and then he started a bake cycle and put his hand in the oven and said it was heating up. However, as we were both looking at the display board and noticing it staying at 100F we felt the element and noticed it wasn't hot/warm at all. He said that it did begin to heat and then it must've cut out, but I don't believe it even began to heat up at all and maybe he just wanted to diagnose it and order the part so he could come back and install it.

He came back the next week and installed the cut-off switch which didn't help. He also connected some wire from the cut-off to some other wire, effectively bypassing this thermal cut-off and that didn't help either. At this point, he took out his voltage wand and started to place near the various relays and cables going into the control board while trying various heating cycles. I witnessed him holding the wand near the bake relay and starting a bake cycle to 400F or something like that, and after starting the bake cycle the wand stayed some color (either green or red) and then after about 4 seconds the color changed to the other color which he told me and I assume means that the relay lost power or failed to deliver voltage from the relay to the heating element. He held the wand near broil relay and started broil cycle and it was a little different. Instead of showing a solid color for several seconds (like it did on bake), it was flickering on one color and continued to do so until we turned the broil cycle off. He said that the broil is getting power but very low power. He said the problem is definitely in the control board and suggested that I send it to one of the two reputable control board repair facilities that his company usually sends boards to as he had never heard of the control board company that I found online and had previously shipped the board to.

I decided to contact the board repair company that I initially shipped to and told them everything from the paragraphs above and they sent me a shipping label to get it back to them for a senior tech to test. I just heard back from them 2 days ago that the board is still testing fine. I believe their standard testing on their test bed is to heat using bake and broil to at least 250F. They've given me the option to pay $120 for preventative maintenance which entails replacing the relays on the board and other component repair/replacement or they can ship the board back to me as-is again.

This is where I dearly need your advice / help! Is there any way that them repairing a board that is already working fine for them will make the oven start working again for me? Should I buy a new element and have someone install it? Or is there something else I should do? Thank you for reading this horror story and for any help you can offer!!
 

rickgburton

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We've had 5 or 6 techs come to look at it/"fix" ..... he took out his voltage wand.....
Freshman class of the "Harry Potter" school of appliance repair??


Should I buy a new element and have someone install it....
Is yours bad? It's easy enough to check it for continuity. Continuity=good No continuity=bad


Is there any way that them repairing a board that is already working fine for them will make the oven start working again for me?
Not an easy question to answer because there's too many variables. If the circuit board company says it's working and everything else in your oven is working properly, then when you install it your oven should work. Diagnosing the problem with that oven isn't rocket science. That oven is actually very easy to diagnose (if you know what you're doing). All the terminals on the boards are marked. You need a DMM (Digital Multi-Meter) and the wiring diagram for that machine. Measure the voltage going into the relay board at L1 and L2. If your meter indicates 220 VAC, set the oven to bake and measure the voltage out to the bake element at L2 OUT and BAKE. Do you have the wiring diagram? I haven't been able to locate one yet. This meter is less than $22 and will take you less than 30 minutes to learn how it works.

DMM (Digital Multi-Meter)
Multimeter-DM10T-01816678.jpg
 

sevencube

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Thanks Rick. I have a multimeter from work so I'll check element continuity. I don't have a wiring diagram but I managed to find a manual so I'll look for that diagram too. I had the company to the preventative rebuild so I'll reinstall this weekend. I know the board has labels on various terminals and relays like BAK, CBAK, etc. Do you know if the board will have labels for things like L1, L2 and L2 OUT or will I need to find their locations from the wiring diagram? Thanks for your instructions. I should be able to make some reasonably informed inferences if it still isn't working when I reinstall it this weekend.
 

rickgburton

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I don't have a wiring diagram but I managed to find a manual.....
The owner's manual won't have any useful information. However, if you found the service manual can you post a copy here? All the terminals should be marked on the board. If you have a part number I can look it up and check for you. Thermador, Viking, Sub Zero and Wolf have made it almost impossible to get any service information from them unless you're an authorized servicer. It's not impossible to diagnose without a wiring diagram and schematic but it is very time consuming as you need to physically trace the wires backwards from the element.
 

sevencube

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So I got the board back with all new relays etc. and the oven still has the exact same issue. I was thinking about looking up how to remove the elements so I can check for continuity but after thinking about it, I realize what maybe the other 5 or so techs noticed which is that it would be too much of a coincidence if both elements (top and bottom) stopped working at exactly the same time. Neither element even starts to heat up regardless of bake, convection bake, broil, or convection roast so I think that's why none of the techs have even mentioned or fathomed a bad element as the root cause.

I also noticed that the big fan in the back of the cooking part of the oven never turns on. This must be a fan that allows the convection heating methods to work by circulating the heat. I don't know if that fan not spinning at all is part of the issue but seems unlikely to me since a standard bake probably doesn't even use that fan at all. I'm assuming it doesn't come on when I do convection bake/roast because it probably doesn't kick on until some certain temperature is reached.

Rather than searching for a wiring diagram at this stage which may be impossible to find anyway, I'm going to start researching on faulty air switch or air switch fan (fairly certain this is not the fan mentioned in the paragraph above). I remember early online research regarding this problem I saw some other Thermador posts about bad air switch or air switch fan and I didn't research enough to find what or where this thing is. I believe it's some fan for internal components and the air switch is some paddle-like thing that moves due to resistance from the fan and if that thing isn't moving then the oven won't heat and similarly, if the fan isn't working to move the paddle then you can't cook. This coincides with the best guess that the board repair people (who admittedly aren't appliance repair people) offered which is that it may be a faulty air switch/fan. If nothing else, I'll reply here if I ever properly diagnose this and find a solution.
 

sevencube

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I also just learned that a relay that is not on the control board, so it hasn't been repaired/replaced yet, is the stall fan relay. It actually is screwed in to the chassis of the oven sitting right behind the control board.
https://www.repairclinic.com/PartDetail/Thermador-Range-Stove-Oven-Relay/00415761/1021680?modelNumber=SMW272YP&ss=a13b115d967504&mr=1

All of the home insurance techs said "relay board or relay switch" is the issue and they weren't able to find the part so they finally gave up and told me my oven wasn't covered. Me being ignorant and not thorough enough with my research, I thought all of the relays were on the control board I've been messing about with for months now.

Rick, do you have any guesses on the probability of this stall fan relay being the issue? If so, I'll try to buy one from the corners of the Internet somewhere.
 

rickgburton

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OK, no need to buy any parts yet until we figure out what the problem is. You're correct, the problem could be the SFR or the air switch or the HTCO or the fan motor. I'll walk you through the testing procedure. I'll try to explain how it works as we go so it will be easier for you to follow. If at any time you don't understand what I'm saying or asking, tell me so we stay on the same page. It's going to be mostly voltage checks at different places. Keep in mind we're doing this without a wire diagram so if I make a mistake I'll let you know as we go. It shouldn't take too long to diagnose the problem even without the wire diagram. I assume you have a DMM and know how to use it. Is that correct?
 

sevencube

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Sure! I'm here. Just to get some more information out of the way, the HTCO was replaced back when I had a local tech come. The first visit he did some stuff and wasn't very thorough and said "it's a cheap part, I'll order and come back next week". He came back and installed it and it didn't fix anything so instead of paying labor I had him remove the new HTCO and put back the one that was originally there. If I can trust this guy any at all then it can't/shouldn't be the HTCO.

Other than that, I'm ready. Do you prefer to help me with this through this thread or some other way? If we get this working it would only be right to pay you for your time and help. Oh, and I do have the DMM here and ready. I used it earlier today when I removed the Bussman fuse and tested for continuity, which it did have.
 
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rickgburton

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sevencube said:
...He came back and installed it and it didn't fix anything......
So instead of taking 1 minute to check it with meter he made two trips and kept you waiting for a week just to tell you that wasn't the problem. Unbelievable !

I found a wire diagram for a similar model.

OK, You have two fans, convection and cooling. The convection fan is in the center of the convection element, back wall center of the oven cavity. We're going to ignore this fan motor for now. We're only interested in the cooling fan motor. All the voltage checks are with the oven set to bake mode. When set to bake, the K8 relay closes. the K6 relay closes and energizes the cooling fan motor. The fan motor must be working for the oven to work.

Fan motor not working: Measure the voltage between COOL and N on the relay board. The meter should indicate 120 VAC. If the voltage is correct, measure the voltage at the fan motor.
relay board-1.jpgCooling fan.jpg

Fan motor working: The air from the fan motor closes the contact in the sail switch. This energizes the SFR closing the contacts. Current flows from L1 through the HTCO, through the closed contacts in the SFR to the DLB relay on the board (L1) and out (DLB) to one side of all the elements. Meter should indicate 120 VAC between DLB and N on the relay board.
relay board-2.jpg

If the voltage is 0, leave one meter lead on N and touch the other meter lead to the COM terminal on the SFR. If the meter indicates 120 VAC replace the SFR
SFR.jpg

If the voltage is correct measure the voltage between L1 and L2 on the relay board. Meter should indicate 220 VAC.
relay board-3.jpg

We probably don't need to go any further.
 

sevencube

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Hey Rick,

So the weirdest thing just happened. I've had the SFR disconnected and sitting on the counter all week with the oven breaker off of course and I just reconnected it plugging the 4 wires back into their terminals -> turned power back on -> set oven to bake and nearly burned my finger by touching the top element which was on. I quickly checked the bottom element too and it was hot as well. Because we weren't expecting the oven to come on and I had the long narrow cover that goes over the door lock mechanism sitting in the oven cavity (still connected to the 2 wires going into the door light button), I had my wife go turn off the power so I could place the cover back where it goes. Also, we were smelling something burning. It wasn't the smell of a wire or electronics burning and it could've been dust that had fallen from that narrow door lock cover onto the lower element, but also because of the smell we wanted to turn off the power to get prepared to try it again. I've tried several times since then but it's not heating up again.

What I've done since then:
-pressed the red button on the HTCO with both the power on and the power off -> still not heating
-disconnected the 4 wires into the SFR again and left it out for about 5 minutes before reconnecting it and trying again -> still not heating

The cooling fan does come on every time I try bake or broil. The sail switch is somewhere out of view correct? So if I can determine that it's bad then I'd probably need to get someone to come service that part you think? I'm ready to measure some voltages based on your diagrams above but I have a couple of questions first.

Your first image related to the cooling fan, relay board-1.jpg, shows the red lead going onto N but not the N with the terminal on it, but the empty N right beside the terminal. Both of these are marked N on my board but the N with the terminal on it is also marked with E2 under the terminal and the N with the 2 empty holes is also marked with E4 under it. I assume I need to actually touch the red lead to the N terminal like you show in relay board-2.jpg but I just want to confirm with you first. Since the fan is coming on I will check the voltage between DLB and N. From there I'll go to the next step depending if it shows 120 or 0.
 

sevencube

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So between DLB and N I'm getting .65V AC on my multimeter. I assume that's close enough to 0 and far away from 120 so I should leave one lead on N and put the other on the COM of the SFR? Does that sound right?
 

sevencube

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Never mind I'm stupid. I forgot you said all voltage checks with oven set to bake mode. So between DLB and N I'm getting 120V and then between L1 and L2 I'm getting 0. However, I left the leads on L1 and L2 for a minute or more and every 20 seconds or so I hear a click between the relays (like I've noticed happening for the past couple of months when troubleshooting the no heat issue) and when I hear that click, the multimeter reads approx. 111 for half a second and then goes right back to 0 until I hear the click of the relays again.

At first I was testing from the wrong L1 (even though your image shows exactly which one to use) but I was testing from the L1 on the farthest right-most part of the board to the correct L2 and that reads 240. But between the L1 and L2 that you wanted me to test I'm getting 0 and then it intermittently jumps to 109-111 for a split second before returning to 0.
 
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rickgburton

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OK, measure the voltage on the relay board between L2 and N. Is it 120 VAC?
relay board-4.jpg

If the voltage is correct, measure the voltage between L1 and L2 at these terminals on the relay board
relay board-5.jpg
 

rickgburton

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If both those voltage readings are correct the problem is most likely the SFR.
 

sevencube

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Between L2 and N I'm getting 118 (calibration is probably slightly off). Between L1 and L2 I'm getting 237. Those voltages seem correct so I should go ahead and order an SFR then? I'm leaning towards a bad SFR too because when I first reinstalled mine today, the oven worked and that's the only thing I changed was took the SFR out for a week and then put it back in today. Seems like as good a time as any to go ahead and order that used SFR I'm thinking?

Thanks again for all your help! I'll definitely be back to report how it goes.
 

rickgburton

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One last voltage measurement just to confirm the SFR is the problem. On the SFR measure the voltage between the NO terminal and cabinet ground ( any cabinet screw or metal surface) and then between COM terminal and cabinet ground. One will show 120 VAC and one will show 0 VAC. If both show 0 VAC the sail switch is the problem.

Either way we isolated the problem. It didn't take us very long to find the problem even though we were troubleshooting through this web site. It shouldn't have taken 5 or 6 techs several weeks and still not find the problem. If you paid that company any money you should be entitled to a refund. That would have taken me or any qualified service tech about 30 minutes to figure out what the problem was. You did an excellent job testing and taking voltage measurements! Well done!

Rick
 

sevencube

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I could measure the voltage between the COM terminal and ground which read 120V and every time the relay would click it would change quickly to something else but would quickly go back to 120V. The NO terminal I can't test because there's no room for me to stick a lead in it while the wire is also connected to it. But hopefully since the COM to ground was 120V, we don't need to test the NO terminal to ground? Is there any way I can get the lead in there to test NO while it's connected. There's not much slack on the SFR anyway. I try to move the control board out of the way as much as I can to pull the SFR out but whatever wires going into it from the back aren't giving me enough to move the SFR all the way to a workable area. Even still I don't see where I could put the lead into the small opening when the wire is plugged in too. :/

I did order the SFR though. I'm hoping it's that because I don't even know where the sail switch is or how to obtain and replace one of those.
 

sevencube

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Hey Rick. I finally got the new (used) SFR after it moved from various different post offices in the town I live in for several days. The bad news is it didn't fix it. Still same issue :(

I'm beginning to think that I need to buy a new oven during the next sale. One last thing I want to check unless you have other suggestions is the HTCO. Would you be able to tell me what I should be looking for when testing it with the multimeter? Also, the little red button on it goes down a little bit when I press on it but I don't feel any haptic click or hear any kind of click. I just assumed that it's resetting even though it doesn't give any indication that I pressed the button other than the button does depress a little bit. Do you know if this is normal or should there be a definite click sound/feel? I even pressed the reset button on the HTCO while trying a baking cycle and it didn't stop the fan from going or stop the display from showing that it was set to bake and was currently at 100 degrees.

Oh I almost forgot. You mentioned sail switch back when we were troubleshooting. Would that happen to be located right behind and a little to the side of where the HTCO is located? There is some part that probably has something to do with the oven door lock (since the door latch seems like if moved enough it will make contact with one of the metal paddles of this part) that I'm not sure what it's purpose is. I can see two shiny metal paddles on it, and the one farthest from the front of the oven can be pressed in and actually gives an audible and haptic click feedback which immediately canceled a bake cycle I was trying when I pressed it. The result of pressing in on that paddle was the same as if I pressed "off" on my oven display panel.

The other question I have is does it matter which of the two terminals the white and yellow cables go on the SFR? The white cable is labeled 107 and the yellow cable is labeled 106. I ask because the SFR I bought on ebay was sent to me with the 4 wires still connected to them but they were snipped off like you can see in these pictures. In the configuration that I found my oven in, the white cable is connected to the terminal nearest where it says "Midtex" but in the used SFR that I received, the yellow cable was the one nearest the "Midtex" text. Basically the two cables were swapped from how my SFR was initially connected. I actually tried swapping those two cables around on my new SFR and my old SFR tonight but it didn't seem to have any effect on anything.
My SFR configurationmy_sfr.jpg

eBay SFR configurationnew_sfr.jpg

Do you think any of this is relevant or more troubleshooting can help us find the root cause. I felt like we got so close and don't really want to give up. Looking forward to hearing from you when you get a chance to look over my update. Thanks Rick!
 
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rickgburton

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sevencube said:
The bad news is it didn't fix it.
No problem my friend, since the relay is a common part to fail on those machines and you obviously got a used one that wasn't checked (wires still on relay), you might have another bad one. It's easy enough to check. Put the machine into bake mode and measure the voltage between the yellow and white wires 106 and 107. If the voltage is 120 VAC you got another bad one. If the voltage is 0 VAC the sail switch is bad (if the htco is good). the sail switch is located in the air path of the cooling fan. Cover must be on the back of the oven for correct airflow. Check it for continuity with your meter on the lowest ohms scale. Push the sail in with your finger to activate the switch. 1=bad 0=good If the switch checks good it's possible the airflow is not pushing against the sail enough to activate the switch so take the two wires off the switch and temporarily short them together and check again for 120 VAC between 106 and 107.


sevencube said:
Would you be able to tell me what I should be looking for when testing it with the multimeter?
Continuity, set your meter on the lowest ohms scale (RX10) or if your meter has a diode check with an audible beep, you can use that function. Remove at least one wire from the HTCO and touch the leads to the two terminals. 0=good 1=bad.
 
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