Oven Thermostat Problem


  #1  
Old 05-28-02, 08:55 AM
DanaM
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Question Kenmore stove, thermostat

Old (1950's/1960's?) Kenmore gas stove, model 103.200910, s/n 1445292, LP gas. Thermostat problem, sometimes works fine, sometimes off by some amount (and works fine if readjusted), sometimes temperature runs away. Temp regulation seems to be via high flame / low flame on burner rather than extinguishing and relighting burner from pilot. (Is this a common arrangement?) The pilot adjustment valves were all shut off, we're lighting the oven and burners manually while the cabin is intermittent use; I'll open the valves and use the pilots once we're there all the time. The previous owner never used the oven and rarely used the range.

The thermostat seems to be "sticking" rather than failing completely, does this sound normal or repairable?

Any idea of the age of this stove?
 
  #2  
Old 05-28-02, 07:25 PM
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Hello Dana. Welcome to my Gas Appliances forum.

The problem description indicates that the thermostat's internal parts are old and the internal bellows are dried out form time and age. The bellows are the parts control the temperature.

When the bellows flexible material dries out, it becomes difficult to control temperature. The only solution is to have the thermostat replaced with a new one.

Replacing a thermostat as a do-it-yourself project may or may not be an easy task on some models. I would not recommended this as a do-it-yourself task, easy or not.

Thermostats that are purchased over the counter and self installed by the do-it-yourself person are not returnable and may not be warrantied by some dealers.

The one item you can check is the capillary tube. That's the heat sensing tube located in the oven compartment. It should be suspended by 2 clips, not bent or damage and not touching anything except the 2 clips.

If the capillary tube is as it should be, I suggest you have the oven checked by a professional. There is no adjustment that can be made to the thermostat to correct the conditions you have described.

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  #3  
Old 05-30-02, 05:36 AM
DanaM
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Thanks for the feedback, Tom. I'll look at the cap tube first, if that's OK I'll pull it apart and see what's what-- I used to design gas stoves for a living though I'm not familiar with this type of thermostat; I worked mostly with small gas cooktops for the marine market.

The bellows is metal, no? Metal does not "dry out". It can work harden if stretched beyond its elastic limit, though even that won't change its elasticity; rather it'll reduce the amount it will flex before failure.

Any thoughts on solving an oven door that is straight when cold, but warps when heated? Hmmm, this well could be related to my problem, as the heat loss through the door causes the thermostat itself to get quite hot.

-Dana
 
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Old 05-30-02, 08:21 PM
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Hello: Dana

The internal bellows are not metal. They are made of leather. They expand and contract. One side is mounted solidly while the other side is attached to the cap tube.

When the vapor inside the cap tube expands {from the heat inside the oven} the pressure pushes a pin [attached to the bellows and the other end is attached to the cap tube].

The movement of the pin pushes the bellows slightly and that movement of the bellows opens a contact switch. The switch cuts off the electrical power going to the glow coil or it may turn off the gas flow to the actuating pilot.

If the cap tube is touching metal inside the oven, it will be sensing an incorrect temp. That causes the oven temp to be slightly off the set temp.

If the cap tube is old, it will lose some of the vapor charge or the leather bellows will become less flexible which will make the ovens internal temp hotter. {Less charge in the cap tube or stiffer leather on the bellows requires more warmer oven temp to increase the pressure on the bellows.

If the oven door is warped or the gaskets are damaged or missing, the oven will not have the ability to control temps as well. This may be all or part of the problem your orginally described.
 
 

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