Really old Lennox furnace .................

I'm curious as to the model number of that unit.

 

Kyle, what electrical measurements have you made and where?

 

That red button appears to be a standard 'bypass the thermocouple safety function button' - used on standing pilot systems to get the pilot lit from cold. Pressing the red button allows gas to flow to the pilot so it can be lit. The little copper tube is an self-contained electrical device which, when heated, then holds open the safety circuit in the gas valve. If the pilot is extinguished the safety circuit prevents any gas from flowing to the burners or the pilot.

To my knowledge pressing that red by-pass button also disables the main gas valve's operation.

What you describe seems contrary to that.

There are two smaller copper tubes - one goes to the pilot I would assume. That seems likely to be the lower one - connected near the red button - although please correct me if I have it wrong. Where does the other copper tube go? The one connected above it and closer to the wiring terminals - where is it's other end?


PHM
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The upper tube is typically a vent and is piped to near the pilot assembly

 

On those early G(H)3 to G(H)9 Lennox models, Lennox rivetted a nice metal tag on the front of their furnaces that gave model number and instructions on how to light the furnace. If that early B53 series ITT (General Controls) combination gas valve is original to that Lennox furnace which I doubt, then that metal tag should outline the operation of that valve.

What is the model number of that furnace, serial number was on a separate sticker.

 

I saved and collected these older metal tags and emblems from the furnaces I removed and disposed of over the years. I went through all my Lennox tags and have this one that appears to have a similar valve with the "RESET" button. The tag shows three different gas valve options the middle one is a fair match. This tag is from a 1957 model.

 

Here's the pic of the rating plate:

(the forum won’t let me post links, so copy and paste the link below and remove “*****”)

https*****://drive.google.com/file/d/1nxOS852PklCOGu70mkQpwIwdXZGmrr7X/view?usp=sharing

Lennox model: GF5-100T

I didn't see the serial number anywhere, but on the rating plate it says it was manufactured on MAR 2 1960.

It also says:

To Light This Appliance
1. open pilot valve and light pilot
2. push manual reset button after pilot has been lighted
3. open main valve
4. set room thermostat indicator to desired temperature

To Turn Off This Appliance
1. close pilot and main valves



Based on the rating plate it looks to me like you have to push the reset button after the pilot has been lit. So theoretically, if someone turned on the pilot valve and lit the pilot but didn't press the reset button the main burners wouldn't come on. If my understanding is correct, after lighting the pilot, the power generated by the thermocouple will not be sent to the gas valve until the red reset button is pushed after a pilot outage.

 

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:eek2:

 

It's Time 😔

 

If he’s is a location with little heat demand and the furnace is still operational then there’s no reason to replace it just because it’s old and inefficient.

 

40¢ on every 💵 probably gos up the chimney

 

Appears to have been manufactured and distributed within the Canadian market. Never seen an (F) in the model. Thank you for taking that picture, pretty cool. It appears that if all things were working properly, once the pilot was lit, the red reset button would have been electrically held down once pressed to maintain main burner operation. It does seem counter intuitive, but this early stuff just having any form of pilot or main burner safety was new technology and changing monthly. Earlier models many I have worked on had no safe guards whatsoever, if pilot went out just raw gas spewing up the flew and same with the main valve, is what it was.

That valve can be replaced with a combination gas valve quite easily. I would reach out to your local furnace guy and verify that heat exchanger is still intact, which it probably is, and if you don't care about efficiencies..like me. You can keep this thing going with a new valve.

Good Luck

 

Kyle,
Are you a technician? If so, please present some evidence of it.

 

That is not a 100% safety shut off. If it was there would be 2 Al pilot tubes coming out where you see the circles in the casting.

It seems like that button would let the valve open when pressed with a call for heat.

Definitely time for an upgrade, just depends on how much you want to upgrade.

 

This was common practice many moons ago.
If pilot light went out the thermocouple would shut off the main gas valve only,
but the pilot gas would continue to allow gas to flow.
The small amount of gas flowing out of the pilot would naturally flow up the chimney.

This setup was only permitted on natural gas.
For LP gas 100% shut off had to be used, shut both main gas and pilot.

 

Yes I am a technician with about 15 years of experience. What are you looking for, my journeyman certificate number? I didn't take voltages or gas pressure because I was looking at my church's furnace off hours. And while that other technical data is good to have, it wouldn't be relevant to my original question.

 

Now we can put this in the proper forum.

 

He should apply for Pro Membership as well 😉

 

I admit can’t recall the part number of that safety device. That was truck stock for me many years ago. Same idea as Baso or General Controls safely that only controled the voltage to to the valve. We all know the pilot gas continues to flow with pilot outage. Never was a problem. When I started in the mid sixties virtually all furnaces were 50% safeties.
I didn’t read where the thermocouple was tested or replaced.

 

Move aside fellas, let the old-timer 'splain it to these kids.

What ya got there is actually two pieces: A General B53-series gas valve and an A100G pilot safety switch. If memory serves, it plugs directly into the valve. Power for the main valve goes to the pilot safety first, if the pilot is out the main valve won't open.

In your setup, to re-light the pilot you turn off the pilot gas and let the chamber clear. That safety is not 100% shut off so there is gas to the pilot all the time, even if its not lit. If you don't let it clear you'll get a surprise when you stick your lighter in there. After five minutes turn the pilot gas back on and light the pilot. You don't hold the button down when you light it. After 30 seconds or so (once the thermocouple gets hot) THEN push the button to reset the pilot safety.

If the unit only runs when the button is being held then either the thermocouple is bad or the pilot safety is bad. Pretty sure no one makes a replacement that will plug into that valve.
So...

If you insist on fixing this thing, you'll need to gut the gas train and put in a combination valve. I recommend the W/R 36C03 series valves. You're probably going to have to "simplify" the wiring too. It'll be a PITA but its doable. Don't forget to put a new thermocouple in.

Fun fact: Baso still offers the L62GB-3 pilot safety. I sell one or two every winter. Sadly it's not a plug in type so I don't think it'll work here.

 

Without going into detail, safety can be bypassed as part of the troubleshooting moment.
The “old-timer” had the models correct that couldn’t recall. I don’t know how many furnaces with 50% safeties I’ve encountered throughout my career with pilot flame extinguished. Never have seen pilot gas accumulate and present a flash. The Western furnaces of the sixties had two flame switch pilots that used approximately one cfh and never were an issue. Just my observations from working on mostly non 100% ignition systems through the 60-70-80’s. Which means so many furnaces we encountered were actually from the forty’s and fifty’s. After 1978 (I believe that’s correct) electronic ignition solved that problem. Sorry for the ramble. Lol