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LG LWS3081ST Wall Oven Cooking Issues


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6 replies to this topic

#1 lgmnguy

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Posted 08 October 2011 - 07:40 AM

I own a two year old LG LWS3081ST wall oven. I have never felt it worked well, preheat times were very long. It seemed that it started to also not cook well, food was uneven.

About 6 weeks ago I turned it on and heard a loud pop and it quit heating. Looked inside and saw a hole in the back wall that covers the element. When I removed the back panel that covers the heating element, I was that the heating element glass cover had shattered and the heating element itself had a portion that was now missing.

So I replaced the heating element and panel that covered it. Turned the oven on and it heated right up, all was well. This past week it started to act up again. Preheats over 400 took a long time and food started to not cook evenly. The problem is betting worse with each use, a batch of cookies refused to cook well last night.

I have not measured the temp inside the oven yet to see if the thermostat is the issue, but I'm also concerned it could be the main board due to all the weird issues. This oven has a power board and a controller board from what I can tell.

Any ideas on the best way to attack this? I haven't called a repair tech since the oven is so easy to repair and I am very good with electronics. My wife is ready to toss the thing, I want to take another shot at it. The thermostat is a $20 part, but the power board is around $250 and the control board $60. I already have $150 into it replacing the element and panel that was burnt.

Thanks

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#2 appl.tech.29501

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Posted 09 October 2011 - 08:43 AM

During preheat the bake, broil and convection fan should be on. If not you will get prolonged preheat times.

Has the unit ever showed a Fault Code?

You can OHM the oven thermistor. Remove the screws, pull it forward disconnect it and it should be
between 1050-1150 ohms @ room temp.
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#3 lgmnguy

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Posted 09 October 2011 - 02:16 PM

During preheat the bake, broil and convection fan should be on. If not you will get prolonged preheat times.

Has the unit ever showed a Fault Code?

You can OHM the oven thermistor. Remove the screws, pull it forward disconnect it and it should be
between 1050-1150 ohms @ room temp.


Thanks for the response. The themistor measured at 1080 ohms, so that seems fine.

Today I did some additional testing with the oven. I put a thermometer inside it and tried some different combinations. If I set it to 350, all is well and it heats up to around 340 (on my thermometer). If I then tell it to go to 425, the oven display immediately says it is at 425. It then takes a long time to go up and finally hit 425 around 20 minutes later.

The convection fan starts when the preheat starts, the cooling fan starts about 2 minutes later.

So I did one final test and I think this may help diagnose the issue.

I started with a cold oven and told it to preheat to 425. It charged up to 383 in a couple of minutes, then the heating element shutoff. The following cycle then occurred:

383 - Heating element off 20 seconds
393 - Heating element comes on for 40 seconds
397 - Heating element off 20 seconds
399 - Heating element comes on for 40 seconds
400 - Heating element off 20 seconds
403 - Heating element comes on for 40 seconds
406 - Heating element off 20 seconds
409 - Heating element comes on for 40 seconds
...etc

So the temp is increasing by 3 degrees every minute, meaning that the preheat took around 2 minutes to get to 383, but then from there took around 10 minutes to reach 425 due to the cycling on and off.

My earlier attempt to go from 350 to 425 had a similar (but even longer result).

So could the controller board be causing this?

Thanks again for the help.

#4 kdog

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Posted 09 October 2011 - 03:41 PM

Since there are 3 elements, and a whole array of cycles (bake,roast,convection cycles etc); having you explain it as "preheated oven and element cycled on and off)" does not pin it down well - have you referred to the user information to discover which elements are to operate in which cycles ?

I am not immediately familiar with your specific model, but can assure you there is nothing like showing up on a service call to read the manual with the owner - some cycles may begin by using all of the elements for preheat, and then cycle one or more of the others to maintain temperature
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#5 appl.tech.29501

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Posted 09 October 2011 - 03:43 PM

the manual doent descibe in full detail how the control operates however,
the rythmic on / off of the element leads me to believe that the control
is working properly and maybe the sensor is getting out of whack.
Most controls will power the element until the sensor tells the control the desired
temp. is reached. This unit should be no different. After the preheated temp. is reached
the conv. fan/element and broil element will turn off and the bake cycling on/off
keeps the oven at the desired temp.

take some sensor readings at different temps say 300, 350, 400.

regardless of the amount of time it takes to reach 425 does it actually
reach that temp and indicate that the preset temp. has been reached?

The convection element should also be on during preheat which it sounds like
it is based on the rapid rise in temp. tp 350F.

The thermostats sould be ok. if they trip they wont reset until the temp. drops
to 14 F.

let us know those sensor readings
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#6 lgmnguy

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Posted 09 October 2011 - 05:24 PM

Thanks for the responses.

You are correct, I didn't explain the heating elements well and actually just learned something.

The element that died and was replaced is the convection element. Odd part of that frying is that we do not do convection baking, so that element was only on during preheat.

There are two other elements, the broiler, and a cooking element that I had no idea existed until you brought it up. I went back to the LG schematic and saw it, I need to hunt it down (it's hidden). I'm using this schematic:

http://c.searspartsd...09085-00003.png

The broiler does work, but I have no idea if it is being used to preheat the oven. The user manual does not discuss which elements are used for the preheat, it only discusses the convection element/fan is used.

Based on the cooking issues we are having, it is not holding higher temps after it finally preheats and my measurement earlier today showed that. At lower temps (350 and below) it is holding much better.

I have a sense of humor about this, I know I'm not trained at oven repair.

#7 kdog

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Posted 09 October 2011 - 10:40 PM

The "hidden" element is likely under the floor of the oven and could be the source of your issue - since you have the schematic, try and locate the wires which travel from the relay board to the element and test the element for continuity, if none - you gonna have to haul it out of the wall to access it
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