Thermocouple - What's this?
#11
My NG hot water heater stopped firing a couple of months ago.  I cleaned the end of the thermocouple and it ran fine until last night.  This morning I removed the burner assembly again and replaced the thermocouple with a standard one you buy at the home center, etc.  Looking at the old one, one end was cut and each end of the conductor was soldered to this device.  

[Image: AMWts8DqwViDsQAFv3PkVaJ7e1ye_EANUs8IY9Sn...authuser=1]

Anyone know what it is and its purpose?  So far, the hot water heater is running fine with the replacement thermocouple.  

Second question, what brand natural gas hot water heater do you recommend?  I've only needed two in over 40 years.  The current one is a Sears, old school, with a standing pilot and vented to my chimney with no damper.  I like it because it's simple, reliable, and required little maintenance for years.  I'm not interested in an on-demand unit.  Thanks.

John
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#12
Looks like a simple resistor
Steve

Missouri






 
The Revos apparently are designed to clamp railroad ties and pull together horrifically prepared joints
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#13
Ours had one of those too...has worked great with a standard replacement.
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#14
(02-07-2023, 03:37 PM)jteneyck Wrote: My NG hot water heater stopped firing a couple of months ago.  I cleaned the end of the thermocouple and it ran fine until last night.  This morning I removed the burner assembly again and replaced the thermocouple with a standard one you buy at the home center, etc.  Looking at the old one, one end was cut and each end of the conductor was soldered to this device.  

[Image: AMWts8DqwViDsQAFv3PkVaJ7e1ye_EANUs8IY9Sn...authuser=1]

Anyone know what it is and its purpose?  So far, the hot water heater is running fine with the replacement thermocouple.  

Second question, what brand natural gas hot water heater do you recommend?  I've only needed two in over 40 years.  The current one is a Sears, old school, with a standing pilot and vented to my chimney with no damper.  I like it because it's simple, reliable, and required little maintenance for years.  I'm not interested in an on-demand unit.  Thanks.

John

I think the thermocouple is there to be heated by the pilot when you first turn it on, so it must be "hot" before the gas to the burners can be activated.

We have had a 40-gallon Rheem Professional NG with pilot light for 13 years now with no problems so far.  One thing I highly recommend is a piezoelectric ignition for the pilot - no more fiddling with a long burning splint, down at about 6" above the floor, and no need for electrical power.  Our heater comes with a feature (called something-Jet) which introduces cold water at the BOTTOM of the tank and withdraws hot water at the top.  This goes a long way to prevent sediment buildup and extends the life of the tank, as well as improving recovery during heavy hot water use.  Every so often I drain a few gallons from the bottom of the tank and have never seen any sediment with this current heater.  The other thing I strongly recommend is to pay attention to the anode rod - with our crappy water the absolute lifetime is about 5 years.
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#15
(02-07-2023, 10:56 PM)GaryMc Wrote: I think the thermocouple is there to be heated by the pilot when you first turn it on, so it must be "hot" before the gas to the burners can be activated.

We have had a 40-gallon Rheem Professional NG with pilot light for 13 years now with no problems so far.  One thing I highly recommend is a piezoelectric ignition for the pilot - no more fiddling with a long burning splint, down at about 6" above the floor, and no need for electrical power.  Our heater comes with a feature (called something-Jet) which introduces cold water at the BOTTOM of the tank and withdraws hot water at the top.  This goes a long way to prevent sediment buildup and extends the life of the tank, as well as improving recovery during heavy hot water use.  Every so often I drain a few gallons from the bottom of the tank and have never seen any sediment with this current heater.  The other thing I strongly recommend is to pay attention to the anode rod - with our crappy water the absolute lifetime is about 5 years.

Yes, of course.  On a standing pilot system like we both have the thermocouple must constantly see heat from the pilot.  If not, it shuts off the flow of gas to the pilot and also prevents the main gas valve from opening when the thermostat calls for heat.  I just have never seen that bit of hardware as part of a thermocouple system.  What that is and what it's purpose is is the root of my question.  

I agree about the piezo starter, so much easier than trying to reach in there with a long match.  You're also right about anode rods.  I replaced the one in my tank after 5 years and it was badly corroded.  I need to do it again - or maybe just buy a new hot water heater since this one has to be at least 15 years old now.  I had one go 30 years though and it never leaked.  

John  

John
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#16
It’s a thermal fuse. It melts at a fairly low temperature. It’s a safety device. The heater is not certified if it’s removed. They are a PITA to find. If the flue was blocked in the heater it would open and shut the unit down. The problem is thermocouples are consumable. Newer designs, if similarly equipped will use a thermal switch that mounts in the thermocouple connection on the gas valve. Standard thermocouple. Some genius also decided to make thermocouples with left hand threads. Another non existent consumable part. Reinventing the wheel.
Blackhat

Bad experiences come from poor decisions. So do good stories. 


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#17
(02-08-2023, 10:40 AM)blackhat Wrote: It’s a thermal fuse. It melts at a fairly low temperature. It’s a safety device. The heater is not certified if it’s removed. They are a PITA to find. If the flue was blocked in the heater it would open and shut the unit down. The problem is thermocouples are consumable. Newer designs, if similarly equipped will use a thermal switch that mounts in the thermocouple connection on the gas valve. Standard thermocouple. Some genius also decided to make thermocouples with left hand threads. Another non existent consumable part. Reinventing the wheel.

Thanks. I knew you probably would know.  That makes sense.  I see replacements on Amazon.  

How does a thermal switch in the gas valve work?  Seems like it would have to be based on the higher voltage being sent and not relying on temperature conducting that far through the TC itself.  If that's correct, the valve itself must trigger on voltages both too low and too high.  

John
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#18
A thermocouple doesn’t conduct heat. Heating the joint between 2 dissimilar metals creates a very small DC voltage. The furnace/water heater thermocouple produces roughly 25 millivolt. Inside the gas valve is a linkage connecting the pilot valve port, the main gas port, the control knob and a small electromagnet. Pushing the knob opens the pilot gas port and depresses the plunger or core of the electromagnet. Thermocouple voltage holds the plunger in place. Voltage disappears and a spring closes the linkage and valve ports. Pushing the button or knob when lighting opens them. The copper tube of a thermocouple is the ground side of the electric circuit. Insulated inside that is the hot wire of the circuit.   Look carefully at the valve end and you’ll see an insulating disc between the copper jacket and that end knob. 

On your thermal fuse, the grounding jacket is cut away but clamped to the bracket each side to close that conductor. The center hot conductor is connected to that lump of low temp solder in the middle. It’s closed until the solder melts. That goes and you can’t get voltage to the gas valve. Pilot will light but won’t stay lit as the electromagnet can’t latch the linkage.
Blackhat

Bad experiences come from poor decisions. So do good stories. 


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#19
Thanks, I made and used hundreds of thermocouples during my lab days.  My question relates to your earlier comment:  "Newer designs, if similarly equipped will use a thermal switch that mounts in the thermocouple connection on the gas valve."  It can't be a thermal fuse like the one near the burner, so it must work on the voltage exceeding some value?  

John  
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#20
It’s a bi metal thermal actuated set of electric contacts. Heat it, it snaps open and then closes when cooled ( hopefully). Switch is placed where desired and wired back to the gas valve. Accomplishes the same thing as your but uses separate components and is resettable
Blackhat

Bad experiences come from poor decisions. So do good stories. 


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