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Old 10-25-2012, 08:07 PM   #106
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Is this old Furnace Able to be Serviced?


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OK, I'm pleading laziness for not going through 7 Pages of postings again.

Beenthere.. What made you think the gas valve was thermopile driven?
Just asking because of the amount of 6 & 12 volt transformers that I've seen attached to dinosaurs, not to mention the look of the extra limit load through that gas valve.
I can see a thermopile down in the pilot light but it could be a thermocouple. I can't tell the difference. There are no tranformers on this dinosaur that I can see. Where should I put my voltmeter to measure the thermopile output and what is the expected voltage for a thermopile?

Thanks in advance, VC

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Old 10-25-2012, 08:46 PM   #107
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Is this old Furnace Able to be Serviced?


Looking at it closer. It does look like a thermocouple system. A thermopile will have 2 wires coming from it.
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Old 10-25-2012, 10:33 PM   #108
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Is this old Furnace Able to be Serviced?


A thermopile will generate about 1/2 volt DC. A Thermopile will be a 1/2 " in diameter whereas a thermocouple will be less than a 1/4"
Thermopiles are usually connected by two wires that are sometimes covered by a spiral wrap that can make them look like one wire. They can have ends that are seperate or ends that screw into gas valves that are identical to thermocouples. I think I saw a spiral wrapped line on the page three photo but it didn't look connected to anything?
Put your meter leads on the black wires connections on the gas valve. Start with a setting above 24V AC. If you don't get 24V,12V or 6V then switch to checking for around 1/2 DCMV.

Last edited by how; 10-25-2012 at 10:54 PM.
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Old 11-05-2012, 01:01 AM   #109
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Is this old Furnace Able to be Serviced?


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A thermopile will generate about 1/2 volt DC. A Thermopile will be a 1/2 " in diameter whereas a thermocouple will be less than a 1/4"
Thermopiles are usually connected by two wires that are sometimes covered by a spiral wrap that can make them look like one wire. They can have ends that are seperate or ends that screw into gas valves that are identical to thermocouples. I think I saw a spiral wrapped line on the page three photo but it didn't look connected to anything?
Put your meter leads on the black wires connections on the gas valve. Start with a setting above 24V AC. If you don't get 24V,12V or 6V then switch to checking for around 1/2 DCMV.
Thanks for your replies. We only had a couple of days of cold so far. It warmed back up so I have been paying much attention to the heater. I think I'll wait until Xmas Eve and all of the relatives are over.

I measured 174mv between the wires shown in the photo below.



When I turn on my thermostat, I have to put a magnet towards the right side of the gas valve. I hear a click and then the burner ignites. Isn't 174mv kinda low for a thermopile?
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Old 11-05-2012, 02:40 AM   #110
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Is this old Furnace Able to be Serviced?


If you want to measure the powerpile output, just do it with the wires from the powerpile. It looks like your measuring points are including the thermostat and gas valve electromagnet. Most furnace powerpile gas valves require at least 250 DCMV and above from a powerpile. Make sure your pilot assy flame is enveloping the powerpile for the maximum possible output and that all your related connections (thermostat, mercury & limit controls) are completely tight.
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Old 11-27-2013, 02:14 PM   #111
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Is this old Furnace Able to be Serviced?


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If you want to measure the powerpile output, just do it with the wires from the powerpile. It looks like your measuring points are including the thermostat and gas valve electromagnet. Most furnace powerpile gas valves require at least 250 DCMV and above from a powerpile. Make sure your pilot assy flame is enveloping the powerpile for the maximum possible output and that all your related connections (thermostat, mercury & limit controls) are completely tight.
It's been awhile since I've addressed this issue here at the forum.
Winter is coming again and this old furnace is still working but I need to go down to the basement and tap on the gas valve with a magnet to fire it up. I'm still trying to determine if I need a new thermocouple or if the gas valve requires more voltage than the thermocouple can provide because it is old and is sticking. I'm hoping it's the thermocouple because I think I can replace that easily & safely for a low price.
I measured 175mv at the thermocouple when its not connected to anything else. Is this enough? When I turn on the thermostat, I measured 130mv at the arrows shown in my last photo. Remember, turning on the thermostat does not open the gas valve. I have to manually assist its opening as I mentioned above. When the thermostat is off, I measured 175mv at the point of the arrows so I know there is not a voltage drop due to poor wiring. Once the gas valve opens and gas is flowing to the burner, I only measure 90mv at the arrow points. I'm wondering if the thermocouple is not producing enough voltage to activate the electromagnets in the valve. I'm suppose I could go buy a larger output thermocouple but I don't want to introduce too much voltage to the electromagnet in the gas valve and damage it. I also have no idea if I need a thermocouple or thermopile and what voltage is needed to open the valve. Thanks in advance, vc
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Old 11-27-2013, 05:36 PM   #112
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Is this old Furnace Able to be Serviced?


thermocouple



thermopile

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Old 11-27-2013, 06:04 PM   #113
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Is this old Furnace Able to be Serviced?


Your thermopile readings are too low.
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Old 11-28-2013, 02:29 AM   #114
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Is this old Furnace Able to be Serviced?


Ok. What should the thermopile voltage be? Is the voltage drop normal when the valve is opened. Thanks, VC
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Old 11-28-2013, 05:21 AM   #115
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Is this old Furnace Able to be Serviced?


You generally don't want to see them less the 500mV. And under load they do drop a lot.
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Old 11-28-2013, 08:58 AM   #116
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Is this old Furnace Able to be Serviced?


you have a thermopile (wires) generator,and a thermocouple (copper capillary tube) to proof the main gas that a flame is present..check all the connection on the generator wiring even the stat a loose connection will pull..but removing the wires and reading are the true generator test..make sure he pilot flame is covering the probe element
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Old 11-28-2013, 07:56 PM   #117
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Is this old Furnace Able to be Serviced?


Thanks for the advice. One of the problems that I have is that I can't actually see the part of the thermopile that is in the flame. I look directly at the flame and actually cannot see how far into the that the thermopile is inserted. If I replace it, I was planning to just disconnect the existing device at the wire nuts, leave it in place and then connect the new device to the wire nuts and somehow clamp it in away that it sits in the flame. Does anyone have a weblink where I can order 500mv thermopile? A brand and model number would be helpful too. Thanks in advance, VC
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Old 12-04-2013, 09:08 PM   #118
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Is this old Furnace Able to be Serviced?


I stopped by the local heating whole sale supplier and picked up the thermopile shown below. It says it will put out 750mv. They guy at the store mentioned that there is a smaller 250mv model that some of the older furnaces used. Mine is an older furnace. I'm just a concerned that that if the coil on the gas valve needs 250mv to open and I energize it with 750mv it could be damaged? What do you guys think? Also, how do I install this thermopile, I cannot figure out where it needs to be installed. Any help will be appreciated. Thanks in advance, VC




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Old 12-05-2013, 05:27 AM   #119
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Follow the cable of the existing one. You'll see where and how its installed. Your gas valve will be marked most likely. A 750mV powerpile doesn't generate 750 mV under load. Not ure I have ever seen a furnace that used a 250mV, maybe a stove.
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Old 12-05-2013, 08:18 PM   #120
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Follow the cable of the existing one. You'll see where and how its installed. Your gas valve will be marked most likely. A 750mV powerpile doesn't generate 750 mV under load. Not ure I have ever seen a furnace that used a 250mV, maybe a stove.
Yes. I took a look and think I can figure out how to make it happen. I suppose that I should turn off all gas to the furnace while making the swap. Do you think it would be fine to just close the pilot light valve?

Thanks in advance, VC

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