Is this "thermo-couple" from my oven ok to use? 1

[william_]

Hi, the attached collection of images—included at the bottom of this post—is referenced in this post.

I was deep-cleaning my Indesit gas-oven. I believe that the parts seen in the attached pictures are called "thermo-couples". One of them is for the grill, the other for the actual oven. They seem to be identical, though I'd appreciate if someone could confirm that.
------------------------------------

One of them seems to be a little damaged, and I just have a couple of questions about it...

The close-up pictures labeled as "D" show the damaged one is a little frayed where its head meets its lead (both picures of "D" are just different angles of the same thing).

Also, the close-up picture labeled as "C" shows that the head of the damaged one is a little crooked.
------------------------------------

Is this damaged thermo-couple still safe to use? I doubt I would be able to find anyone to repair it. If it isn't safe to use, then I could just not use the grill, and use the other one with the oven, so long as they are indeed identical.

 

[IRstuff]

It's not a question of safe; I don't think it will work at all. These thermocouples are used to turn on the main gas supply for the burners, but they depend on the thermal expansion to push the valve open. If the casing is broken, the thermocouple has no fixed point to push against.

 

[3DDave]

Not so much a thermocouple as a thermally operated actuator?

That's a lot of friction multiplying bends in the housing but maybe that was the problem. Hard to tell with the pixel shortage.

 

[waross]

It's not a question of safe; I don't think it will work at all. These thermocouples are used to turn on the main gas supply for the burners, but they depend on the thermal expansion to push the valve open. If the casing is broken, the thermocouple has no fixed point to push against.

What a wild flight of fancy.
I hope you know more about aerospace than you do about thermocouples.

 

[waross]

If it works it's okay.
No safety issue.
If it shorts there is not enough current do do any damage.
If if goes open, the gas won't turn on.
To test, put the hot end in a flame and check for either voltahe or current at the connector. There should be a potential between the center contact and the outer sheath.
You need a sensitive meter.
You will be looking for milli-amps or milli-volts.
The biggest danger:
You have a lot of friends over for a barbeque and the connection is disturbed and fails, spoiling your party.

 

[3DDave]

It should be the case that there is a complex circuit board that is designed to detect either a short circuit or an open circuit on the thermocouple and will prevent the oven from operating with either defect. I think the outer sheath that is fractured is tied to common ground. Breaking this connection will still let the circuit board to detect the completed circuit via an alternative path, but the measurement may be incorrect.

 

[dik]

I hope you know more about aerospace than you do about thermocouples.

I thought his explanation was plausible... they appear to be actuators as 3DD noted.

 

[waross]

Sorry. No actuator.
No circuit board.
Google thermo-couple.
The copper tube is actually a co-axial cable.
The different material inner conductor is a different material from the sheath.
Atemperature difference between the hot end and the connection end will develop enough EMF/current to hold in the pilot gas valve solenoid.
All failure modes result in the pilot gas valve not openning.
There may be more sophisticated applications but in all cases if works it's okay.
If it's damaged, to the point that it won't work, then replace it

 

[3DDave]

There are photos of thermocouples that look identical to the device in the original post, complete with the insulator washer at the control end. I was commenting on the supposition it was a therm-mechanical and thought it unlikely from the number of bends.

Anyway, the parts are generally inexpensive and this one has clearly broken to the point of uselessness and could be replaced, likely for under 30 Euros.

 

[waross]

There is no need for protection.
In the case of a short circuit the current will be to little to do any damage.. The thermo-couple just won't work and the gas won't turn on.
In the case of an open circuit the voltage will be to little to pose any danger. The thermo-couple just won't work and the gas won't turn on.

 

[Compositepro]

This thermocouple generates a low voltage current that can hold the main gas valve latched open after the pilot light has gotten it hot enough. Its only purpose is to delatch the gas valve to the closed position if the pilot light goes out. These thermopiles only cost about $10 and can be bought at most hardware or appliance part stores, or Amazon. You just have to get the right one that will fit. Search for:

MENSI Gas Thermocouple Kit M6x0.75 with Universal Adapter Nuts Replacement 900mm Long M9x1-M10X1 on Amazon.com​

These are not capillary tubes filled with a liquid that thermally expands and moves a diaphragm that actuates an electrical switch or gas valve. Those are used for controlling oven temperature.

 

[william_]

This thermocouple generates a low voltage current that can hold the main gas valve latched open after the pilot light has gotten it hot enough. Its only purpose is to delatch the gas valve to the closed position if the pilot light goes out. These thermopiles only cost about $10 and can be bought at most hardware or appliance part stores, or Amazon. You just have to get the right one that will fit. Search for:

MENSI Gas Thermocouple Kit M6x0.75 with Universal Adapter Nuts Replacement 900mm Long M9x1-M10X1 on Amazon.com​

These are not capillary tubes filled with a liquid that thermally expands and moves a diaphragm that actuates an electrical switch or gas valve. Those are used for controlling oven temperature.

Thank you so much for that recommendation. I got this one in the end

https://www.amazon.co.uk/dp/B073QJVXWV?ref=ppx_yo2ov_dt_b_fed_asin_title

 

[william_]

It's not a question of safe; I don't think it will work at all. These thermocouples are used to turn on the main gas supply for the burners, but they depend on the thermal expansion to push the valve open. If the casing is broken, the thermocouple has no fixed point to push against.

Thank you! It's funny, I'm almost certain the damaged one was being used with the actual oven (as opposed to the grill), and I had been using the oven without a problem...

 

[william_]

If it works it's okay.
No safety issue.
If it shorts there is not enough current do do any damage.
If if goes open, the gas won't turn on.
To test, put the hot end in a flame and check for either voltahe or current at the connector. There should be a potential between the center contact and the outer sheath.
You need a sensitive meter.
You will be looking for milli-amps or milli-volts.
The biggest danger:
You have a lot of friends over for a barbeque and the connection is disturbed and fails, spoiling your party.

Thank you so much for that.

 

[william_]

It should be the case that there is a complex circuit board that is designed to detect either a short circuit or an open circuit on the thermocouple and will prevent the oven from operating with either defect. I think the outer sheath that is fractured is tied to common ground. Breaking this connection will still let the circuit board to detect the completed circuit via an alternative path, but the measurement may be incorrect.

Thank you. I didn't find any circuit-board while dismantling the oven though, not even in the power-supply box.

The oven is about 20 years old though, and has been made obsolete by Indesit.

 

[william_]

Sorry. No actuator.
No circuit board.
Google thermo-couple.
The copper tube is actually a co-axial cable.
The different material inner conductor is a different material from the sheath.
Atemperature difference between the hot end and the connection end will develop enough EMF/current to hold in the pilot gas valve solenoid.
All failure modes result in the pilot gas valve not openning.
There may be more sophisticated applications but in all cases if works it's okay.
If it's damaged, to the point that it won't work, then replace it

Thank you.