Gravity furnace problem - Fiberglass RV


Reply
 
Thread Tools Search this Thread Display Modes
 
Old 06-23-2014, 08:29 AM   #1
Member
 
Name: THOMAS
Trailer: 1972 COMPACT JR
Colorado
Posts: 46
Gravity furnace problem

During last winter I purchased my "new" 1972 Compact Jr. Have almost completed my re-doings and repairs. One major thing left to do. The furnace is the original gravity "Comfy" brand (don't have the model number with me right now). Need to take care of this before winter here in Colorado.
The pilot light works fine and the main burner comes on in quite a normal mode. (BTW, I have already removed the furnace, cleaned the burner, and reinstalled it). However, the main stays on for only about 10-12 seconds and goes off, and so does the pilot light. Since it is a gravity furnace there are no moving parts. I can re-light it repeatedly and it does the same thing.
I have to believe that the thermocouple for the pilot light is okay. However, at the bottom of the furnace there is a HUGE thermocouple-looking device that appears to be an integral part of the gas valve, unlike the pilot-light thermocouple which is easily replaceable. Don't know exactly what that is but I think that part is the culprit. Anyone have a solution for me, other than replacing the main gas valve? If replacement is the answer, GOK if there is a direct replacement is available. Tnx for any help/advice....Tom J.
__________________

__________________
THOMASJU is offline   Reply With Quote
Old 06-23-2014, 09:27 AM   #2
Senior Member
 
Name: Darwin
Trailer: 2002 19 ft Scamp 19 ft 5th Wheel
Posts: 3,030
Send a message via Yahoo to Darwin Maring
I think that big thermocouple gets hot and actually moves a device at the opposite end (The mechanical thermostat). I had one like that on a small tabletop oven.
__________________

__________________
Darwin Maring is offline   Reply With Quote
Old 06-23-2014, 11:30 AM   #3
Senior Member
 
mszabo's Avatar
 
Name: Mike
Trailer: 1986 Bigfoot FT20
Michigan
Posts: 650
Thomas, there is clean and there is clean. I'll bet you have spider nest in both the burner and thermocouple tubes.
Those nest are so sticky gas won't flow through them.
Air alone won't do it.
__________________
mszabo is online now   Reply With Quote
Old 06-23-2014, 12:03 PM   #4
Senior Member
 
Roy in TO's Avatar
 
Name: Roy
Trailer: 1972 boler American and 1979 Trillium 4500
Ontario
Posts: 4,954
Quote:
Originally Posted by THOMASJU View Post
Need to take care of this before winter here in Colorado.
The pilot light works fine and the main burner comes on in quite a normal mode. (BTW, I have already removed the furnace, cleaned the burner, and reinstalled it). However, the main stays on for only about 10-12 seconds and goes off, and so does the pilot light. ...

I have to believe that the thermocouple for the pilot light is okay. However, at the bottom of the furnace there is a HUGE thermocouple-looking device that appears to be an integral part of the gas valve, unlike the pilot-light thermocouple which is easily replaceable.
Winter in Colorado? I just heard some parts got snow last week!

Will the pilot light stay on for extended periods of time? Like an hour or so?

The HUGE thermocouple is what calls for heat, that shutting off the gas to the main burner should not affect the pilot light. Some furnaces have an adjustment screw for for the pilot light, you might want to try adjusting that. It is usually a needle valve, that may need cleaning.
__________________
Roy in TO is offline   Reply With Quote
Old 06-23-2014, 07:29 PM   #5
Member
 
Name: THOMAS
Trailer: 1972 COMPACT JR
Colorado
Posts: 46
OK....just left the pilot light on for thirty four minutes. Then turned the gas valve to the "on" position and the main burner came on. Then it went off after 10 seconds or so and took the pilot off with it. Don't see how that could be spider webs/nests, but I see what you are saying. Any point in taking the gas valve apart to perhaps find something? Probably too hazardous when I put it back together again. Local RV parts guy said he could get a new valve for approx. $200.00. OUCH ! ! I AM "mechanically inclined", having been in home/appliance maintenance nearly all my working life (now 76 years old).
__________________
THOMASJU is offline   Reply With Quote
Old 06-23-2014, 08:46 PM   #6
Senior Member
 
Name: None
Trailer: None
None
Posts: 2,736
Check the size and position of the pilot flame (main burner off) and compare it to the size and position of the pilot flame when the main burner is on . Low/high gas pressure / exhaust draft can cause the pilot flame position to vary . The pilot flame may not be hitting the thermocouple properly when the main burner is on
__________________
steve dunham is offline   Reply With Quote
Old 06-23-2014, 09:46 PM   #7
Member
 
Name: THOMAS
Trailer: 1972 COMPACT JR
Colorado
Posts: 46
Thanx, Steve.....I'll ck that tomorrow morning.

TJ
__________________
THOMASJU is offline   Reply With Quote
Old 06-24-2014, 08:36 AM   #8
Member
 
Name: THOMAS
Trailer: 1972 COMPACT JR
Colorado
Posts: 46
Steve...It is now "tomorrow" morning and I checked the furnace in the manner you suggested, three times. Pilot light stays "exactly" the same after main burner is on. Same results....after a few seconds the main burner goes off, taking the pilot light off with it.
If the HUGE t'couple is the one which controls the t'stat, I wonder why the main doesn't just go off and leave the pilot alone...
Something internal to the gas valve I guess.
I'll wait a day or so before I pull the furnace, clean the burners again (both pilot and main) before I think more about taking the gas valve apart and check it out/attempt to clean its innards and see what
trouble I can get into. I WILL NOT compromise my safety just to save $200.00. TJ
__________________
THOMASJU is offline   Reply With Quote
Old 06-24-2014, 10:22 AM   #9
Senior Member
 
Name: None
Trailer: None
None
Posts: 2,736
Does the main burner light right away when calling for heat or is there a slight delay and noise when the main burner lights ? If the combustion chamber is warped or damaged sometimes gas builds up in the firebox and when the main burner finally lights it will screw up the pilot flame and shut down the fuel supply.
__________________
steve dunham is offline   Reply With Quote
Old 06-24-2014, 10:30 AM   #10
Senior Member
 
Carol H's Avatar
 
Name: Carol
Trailer: 22' Airstream Formerly 16' Scamp
British Columbia
Posts: 11,731
Registry
Quote:
Originally Posted by THOMASJU View Post
Local RV parts guy said he could get a new valve for approx. $200.00. OUCH ! ! I AM "mechanically inclined", having been in home/appliance maintenance nearly all my working life (now 76 years old).
Be thankful (then again maybe not) that they are willing to get you a new valve regardless of the cost. We have a number of RV shops here who have flatly refused to work on or bring in parts for old gravity feed furnaces (assuming yous is the same age as the trailers) for fear of liability issues.
Carol H is offline   Reply With Quote
Old 06-24-2014, 11:27 AM   #11
Senior Member
 
David Tilston's Avatar
 
Name: Dave W
Trailer: Trillium 4500 - 1977, 1978 (2), 1300 - 1977, 1973, and a 1972
Alberta
Posts: 5,317
Registry
I have never taken apart a gas valve in a gravity furnace. The temperature control seems to use gas pressure to turn the fuel on and off. I assume it is at least as complex as an old clock. It would be nice if they could be repaired.

What I would like to try is transplanting the gas valve from another gravity furnace. I suspect that the orifice of the valve is dependent on the Btu rating of the furnace, so I would try to match up the Btu values, or find a way to change the orifice.
__________________
David Tilston is offline   Reply With Quote
Old 06-24-2014, 02:21 PM   #12
Senior Member
 
mszabo's Avatar
 
Name: Mike
Trailer: 1986 Bigfoot FT20
Michigan
Posts: 650
Thomas, when you check it again make sure the bees haven't setup shop in the exhaust side of the furnace.
If the heat exchanger fills with CO2 it will put out the flame also.
__________________
mszabo is online now   Reply With Quote
Old 06-26-2014, 11:38 AM   #13
Member
 
Name: THOMAS
Trailer: 1972 COMPACT JR
Colorado
Posts: 46
Re post #9
No, Steve, that doesn't happen. I'll take the furnace out and re-clean the burner (poking something down into all the burner orifices) and see what happens. TJ
__________________
THOMASJU is offline   Reply With Quote
Old 06-26-2014, 12:57 PM   #14
Senior Member
 
Name: Darwin
Trailer: 2002 19 ft Scamp 19 ft 5th Wheel
Posts: 3,030
Send a message via Yahoo to Darwin Maring
A pipe cleaner works really well. The kind of pipe a person smokes.
__________________

__________________
Darwin Maring is offline   Reply With Quote
Reply

Tags
furnace


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Duo-Therm gravity furnace not working properly Rick G Problem Solving | Owners Helping Owners 9 12-08-2015 05:46 PM
Duo-Therm Gravity furnace manuals Raya Care and Feeding of Molded Fiberglass Trailers 23 07-16-2011 04:16 PM
exhaust grate for gravity furnace on 1972 Boler Cheryl Lee Care and Feeding of Molded Fiberglass Trailers 1 06-25-2009 03:57 PM
REMOVING a DuoTherm gravity furnace Marv Watson Problem Solving | Owners Helping Owners 5 06-08-2009 06:57 PM
Duo-Therm Gravity Furnace Jake Jacobson Classified Archives 1 11-10-2008 04:13 PM

» Upcoming Events
No events scheduled in
the next 465 days.
» Virginia Campgrounds

Reviews provided by


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 12:05 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.