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  #1  
Old 10-15-2013, 06:59 PM
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Gas forced air furnace question

Got two 1956 gas forced air furnaces in a rental. Both have the same problem--no gas flowing to the burner. Both have identical gas train systems--manual valve with an outlet for a pilot, gas valve with a thermcouple going to the pilot, then an electric solenoid activated by thermostat to release gas to the burners. Have gas up to the inlet side of the gas valve but no gas coming out the outlet towards the electric solenoid valve. Assumed it was the thermocouples. But I swapped in new thermocouples and still no gas. I have gas at the valve because I can pull down on the gas check thingy at the bottom and gas comes out. But nothing is going thru to the solenoid. Any ideas out there? Gas was shut off for a while over the summer and I figured this caused the failure of both thermocouples since they had been hot for about 25 yrs at least.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
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  #2  
Old 10-15-2013, 07:02 PM
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Did you keep the pilot lit for a few minutes before checking this? It takes time for the thermopile to warm up enough to hold the gas-valve open.
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  #3  
Old 10-15-2013, 07:05 PM
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Bet things all cucked up inside the body...like o rings on the gas valve and such..moisture...??

Or like Spdrun said...
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  #4  
Old 10-15-2013, 07:07 PM
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Those little buggers do go bad due to the thermal cycling they're prone to.

I've had mine go out three times since '91.

Expecting the next one either this winter or next...

Ahhhh...the price we pay for convenience.
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'10 - Dakota SXT - Daily Ride / ≈ 172.5K
.'76 - 450SLC - 107.024.12 / < .89.20 K
..'77 - 280E - 123.033.12 / > 128.20 K
...'67 - El Camino - 283ci / > 207.00 K
....'75 - Yamaha - 650XS / < 21.00 K
.....'87 - G20 Sportvan / > 206.00 K
......'85 - 4WINNS 160 I.O. / 140hp
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  #5  
Old 10-15-2013, 07:09 PM
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Thermocouple was in the flame for 5 minutes or more with no response. Maybe the valve itself is sticking.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #6  
Old 10-15-2013, 07:47 PM
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Well, that's weird, I guess you learn something new everyday. I've owned that place for 24 yrs and I didn't know. When the gas goes off, after you light the pilot, which is controlled by a manual valve, there's a red ring around the base of the first gas valve. You have to close the main gas valve, pull that ring down and then re-open the gas valve in order to get the gas to flow again.
I had pulled that ring down with the power to the furnace and gas flowed out around it. I had then pulled it down with the power off and no gas came out which I thought was weird. I then read the instructions on the plate on the furnace and it refereed to a 'safety ring' and how to activate after lighting the pilot. When I did, everything was back to normal. Anyone ever run across a feature like that before?
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #7  
Old 10-15-2013, 10:53 PM
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Yeah.....and read the instructions too.....makes things so much better after pulling ones hair out.

Been there, done that.
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The Constitution does not permit impeachment because the House finds the president loud, dislikes his policies or simply regards him with uncontrollable, pathological, stammer-inducing hatred. Nonetheless, Democrats despise Trump and are determined to impeach him, no matter what.

Sent from my Mothers basement using an old fashioned keyboard.
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  #8  
Old 10-16-2013, 12:07 AM
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Unless I'd have spent an hour messing with the thing trying to get it to work, I'd never have understood what the cryptic instructions about a 'safety device' referred to.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #9  
Old 10-16-2013, 07:22 PM
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The safety device is the red ring at the base of the pressure regulator. Anyone seen anything like that before? Talked to a HVAC friend of mine and he hadn't heard of it.
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Gas forced air furnace question-furnace-safety-valve.jpg  
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #10  
Old 10-16-2013, 07:59 PM
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The original furnace in my mom's house (built late 50s) had that. We had to replace it in the 80s because it had a cracked plenum, I'm surprised both of yours have made it this long.

I have no idea what the brand was, that was a long time ago.
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  #11  
Old 10-17-2013, 08:09 AM
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I'm impressed that any furnace that old is still running. I doubt if they build them like that anymore.
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  #12  
Old 10-17-2013, 10:21 AM
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Me too. Its simplicity adds to its longevity. I have replaced the bearings on the blowers and a motor.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #13  
Old 10-17-2013, 01:08 PM
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Old stuff was built before they knew how to engineer something to last til the end of the warranty. I had old AC units on my previous building that were at least 50 years old and kept running. A capacitor here or there and they kept going. Prolly not real efficient but the tenants paid the electric.
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  #14  
Old 10-17-2013, 01:17 PM
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Quote:
Originally Posted by Skippy View Post
I'm impressed that any furnace that old is still running. I doubt if they build them like that anymore.
I heard the same thing about cars in the 80s when I was growing up, yet my 240D is 30 years old and still tickin' along. FWIW, my parents have a townhouse built around 1950. Until they decided to put in central A/C, the house had the original forced air furnace, and it worked fine. You had to change the fan belt once every few years, but that was about it.
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  #15  
Old 10-17-2013, 02:19 PM
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When it comes to NG, even IF the instructions are there, IF there's just ONE THING that doesn't make sense (considering some of these instructions are written in Jinglish or some form of Hackedup-Chinese...), I defer to the experts in NG installations or maintenance.

I like my roof on my house, not in my neighbor's yard.

Then, when the expert(s) arrive, I hang on to their every word about starting the thing and maintaining.

Otherwise, it's another "service call" expense.

I'm not a big fan of NG (even propane tanks give me a severe, internal, case of heeby-geebies).

But, when it's simple, common sense, caution and proper handling are easier to work with than just plain hacking away at it 'til "something happens."

Those are the times I hope I've walked away from...

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M. G. Burg
'10 - Dakota SXT - Daily Ride / ≈ 172.5K
.'76 - 450SLC - 107.024.12 / < .89.20 K
..'77 - 280E - 123.033.12 / > 128.20 K
...'67 - El Camino - 283ci / > 207.00 K
....'75 - Yamaha - 650XS / < 21.00 K
.....'87 - G20 Sportvan / > 206.00 K
......'85 - 4WINNS 160 I.O. / 140hp
.......'74 - Honda CT70 / Real 125

.
I didnt really say everything I said.
. . . . . . . . . . . . . . . . . . ~ Yogi Berra ~
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