haze5736
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1970 Fan Lee Liner 16'
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Post by haze5736 on Dec 18, 2020 14:07:35 GMT -8
I wanted to share my experience repairing a Duo-Therm 11HLU gravity furnace. There was not a lot of information out there, so hopefully this will help someone else down the line.
My furnace still worked with the exception of the thermostat. So I could light the furnace and it would come on but I could not regulate the temperature. It was either on or off. There was no longer any resistance when turning the thermostat and no longer that distinctive click when going from off to a setting that would command heat. We don't camp in extreme cold so we were turning it on before bed to get the camper warm then shut it off at bed time hoping to make it through the night. If it was really cold (30F or just under) I would wake up in the middle of the night, cold, and would run it for a short time.
My original gas valve has an identifier on it, TV17AA10. I didn't know this when I was researching because at that point I had not removed the original gas valve to be able to see it. I believe I found something on the Robertshaw website that said this original number crossed to a Robertshaw 710-201. I originally found this out after hours of searching the web. I found a Duo-Therm document that showed the original gas valve part number of 41-0640. I can't remember the site but one crossed this number to the Robertshaw 710-201.
The instructions that came with the replacement valve noted that a conversion kit was required for LP use. That part number is 1751-013. Although, the part number on the box I received is 1751-01C. The ebay listing did advertise it as a 1751-013.
Two of the ports on the new gas valve are in different locations so some tubing bending was required. The pilot gas line and the thermo-couple line needed to be gently manipulated. Luckily the length on both tubes was ok to reach the new locations. The pilot gas line needed to be bent 90 degrees in the opposite direction as well as curved to meet the new location. I had to work very slow and careful to avoid kinking or breaking the tube.
I finished by purging the air out of the system then used soapy water to look for leaks. And ,of course, my inlet was leaking so a couple slight turns of the nut and no more leaks.
The hardest part of the whole process was the research.
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ekimnamniets
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Post by ekimnamniets on Dec 19, 2020 7:05:19 GMT -8
Any chance of a posting pic of your furnace? I have a Duo-Therm furnace but unsure of the model. Thanks.
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70popup
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Post by 70popup on Oct 10, 2021 16:12:48 GMT -8
Hi, I'm new to the forum. I have a 70 wheel pop up that I acquired last winter, and after some minor repairs and cleaning over the summer I am planning on a couple small trips this fall. The furnace is a Duo-therm model 12 mhu, which lights and fires up properly. The thermostat is a numbered dial from off to 5 that doesn't seem to work. When the gas valve is turned from pilot to on it fires up but the thermostat does nothing. I hear a click sound when i turn the knob a few numbers, but no change in the flame. It has the capillary tube and wire type probe for temperature, and i am wondering if this or inside the gas valve is the problem. I have noticed that as the furnace runs a while the numbered dial clicks at a higher number, like it is sensing the temp but still no change in operation. The probe is mounted on the side of the valve, which seems to be correct. Any advice greatly appreciated, meanwhile i can use the furnace but no thermostat function.
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Post by vikx on Oct 10, 2021 21:06:23 GMT -8
It sounds like the probe or tubing to it may be faulty. The tube goes INto the valve, so who knows where it might have failed? The click tells me the knob is OK. The big drawback to using the furnace is that you have to watch it all the time. You certainly don't want it to overheat!
A lot of us replace the heaters with Wave 3 catalytic heaters, which work well. They are miserly on propane, too.
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70popup
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Post by 70popup on Oct 11, 2021 4:57:12 GMT -8
Thanks for the info. I will probably just get by with it this fall, if I get to do any camping and the nights are cold before I can get a better look at it. Anyone know if there is a way to test that temp probe/bulb? I would like to repair the furnace and keep it in use as it is original and in decent physical shape. I do have some general knowledge of these heaters but
i would appreciate learning more
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Post by vikx on Oct 11, 2021 9:31:39 GMT -8
Even in the old days, they would have replaced the valve with bulb. I don't think there's really a way to test it. I've known people who have "rebuilt" the valve but it's tedious to do. I don't think you can test them separately; once the bulb or tube is disconnected or damaged, no way to reconnect. You could also inspect the bulb and tube closely to see if it's lost the fluid. If it has, it's done.
One thing that comes to mind is the amount of time you're giving the heater to turn on and off. Turn it on low, then wait 5 minutes to see what happens.
These old heaters are very useful and it's a shame to lose one. You might look for a company that specializes in gas valves. Most operate the same way, doesn't really matter what it's controlling; even a stove company. Another option is hunt for a replacement valve.The days of replacements or parts are fading away...
Try Trailertrasher1 at gmail dot com. A picture goes further than the old model #. Keep us in the loop.
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70popup
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Post by 70popup on Oct 11, 2021 19:53:07 GMT -8
Thanks for the advice. I did get a chance to check out the temp bulb/probe but didn't see any obvious concerns. Like you said though, it's most likely bad because even with the thermostat dial in the off position the heater fires up. I would say I let it burn about 5 mins on low setting and no change.
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