Troubleshooting Your Furnace: Why Your Pilot Light Keeps Going Out

[trader4]

It takes two connections to make a circuit. Each of those two is one of them.

[Stormin Mormon]

Most thermocouple I've seen, have one copper tube, and the electrical is pin and shield. Might this themocouple have two wires? I've never see none like that. But, most 1969 equipment near me has long since been replaced.

Christopher A. Young Learn more about Jesus

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It takes two connections to make a circuit. Each of those two is one of them.

[trader4]

I just took a look at my water heater and you're right. The thermocouple is just one nut connection. It's been a long time since I replaced one and I guess the two connections thing I had in my mind was from the two connections I needed to take off apart to do the repair. One was the TC, the other the pilot light gas line.

So, what he has is a mystery. When he removes it and looks at it should be easy to determine if it's one TC or two. Depending on the climate where that 1969 furnace is located, it might be time for a new one. Can't imagine the efficiency of that beat. I replaced by 25 year old gas furnace two years ago. It made a huge difference in gas bills.

[Bob_Villa]

NEVER tell a top-posting Mormon he's right...that's NUTS!

[clare]

Nope. The thermocouples are CoAxial connectors.

[themattfella]

Now I see that the 1/8" copper line that has a 3/8" nut is the thermocouple.

The other 1/8" copper line has a 5/16" nut holding it to the valve body. Upon closer inspection, I find that it is a copper tube that is open on the end. About 2 1/4" from the open end, there is a 3/16" OD brass ferrule.

The ferrule can't be slid on the tubing easily. There is a clamp on the outside of the metal pilot box that looks like it could hold the tube in place, but the clamp is loose, and it was not holding the tube, not securely anyway.

What is the function of this open-end tube, and how should the end be situated when I reassemble it?

BTW I am in the Midwest, and the input rating is 110,000 Btu/hr. The aluminum pilot tube was replaced a couple years ago at a cost of about $100 when it did not need it. I am assuming that the reassembly was incorrect.

[Stormin Mormon]

Thanks for going, and taking the time to look. With a unit that old, I was totally willing to belive a two wire thermocouple.

Christopher A. Young Learn more about Jesus

.

I just took a look at my water heater and you're right. The thermocouple is just one nut connection. It's been a long time since I replaced one and I guess the two connections thing I had in my mind was from the two connections I needed to take off apart to do the repair. One was the TC, the other the pilot light gas line.

So, what he has is a mystery. When he removes it and looks at it should be easy to determine if it's one TC or two. Depending on the climate where that 1969 furnace is located, it might be time for a new one. Can't imagine the efficiency of that beat. I replaced by 25 year old gas furnace two years ago. It made a huge difference in gas bills.

[Stormin Mormon]

I'll be picking flowers off the wall paper for weeks.

Christopher A. Young Learn more about Jesus

.

NEVER tell a top-posting Mormon he's right...that's NUTS!

[Stormin Mormon]

What if two thermocouples want to live together, but not be married. Would that be commonlaw coaxial cohabitation? That's a conundrum. Do you concur?

Christopher A. Young Learn more about Jesus

.

Nope. The thermocouples are CoAxial connectors.

[Vic Smith]

Look for a part number on the gas valve, cross reference that with your furnace model number, and search the internet. Some here might do the search for you if you provide the numbers. Otherwise, it's just shooting in the dark - and maybe dangerous. There's lots of gas valves and different setups.

[themattfella]

Okay, I looked closer at the valve, and the open-ended copper tube is attached to a port on the valve marked "VENT".

What is the purpose of that vent?

The valve bears the number B57RB67. It seems that perhaps it can be replaced by Robertshaw 720-402.

[Vic Smith]

The first answer to this question is probably your answer.

[Tony Hwang]

Hi, First of all, your furnace sounds very old having a pilot with low efficiency. And pardon me, looks like you haven't got a clue what you are upto. Often there is a adj. screw under a plug on the valve body for pilot flame size and if the thermocouple connection is tight, just re- place it. And adj. pilot flame size proper - Done.

[Tony Hwang]

Or your line feeding the gas to the pilot is plugged up piano wire is good for unclogging.

[clare]

The "vent" is to vent any gas that might leak from the valve assembly to the pilot where it will burn harmlessly -and in normal use apply atmospheric pressure to the atmospheric side of the regulator (if so equipped)

[krw]

If they're going to cohabitant, I certainly hope they do. You wouldn't want little bastard thermocouples running around, would you?

[clare]

Unlikely if he has a good blue pilot flame as reported.

[nestork]

Themattfella:

My understanding is that old gas valves had "vents" which vented small quantities of gas into the pilot light. However, if your pilot light assembly has been replaced in the past 20 years, you probably won't have anywhere to connect that vent line to.

I can't see what you have there, or how it's all supposed to fit together, but you need to put things back together so that the end result is that anything coming out the end of that vent tube gets burned in the pilot light. You might even have to hold things together with some bare copper electrical wire or the steel wire in twist ties to accomplish that, but looks don't matter. As long as you burn any gas that comes out of that vent tube, that's all that matters.

[themattfella]

Yeah, good. Okay thanks, Vic and Clare.

I'm ready to go ahead with the replacement of the thermocouple now.

And now it seems that the last guy to work on this didn't get the vent properly situated in the pilot flame.

Also I will be shutting off gas to the furnace from June 1 to October 1 or so.

Thanks for all of the helpful replies.

[Tony Hwang]

Hi, OP said click and pilot goes out after couple mins. TC output drops and gas supply to pilot quits. Replace the damn TC which is not really expensive. Some more thought? Pilot flame positioned wrong, chimney draft? What else is left?