Heater won't start automatically - Fiberglass RV


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Old 09-22-2012, 01:47 PM   #1
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Name: Rick
Trailer: planning to move up from aluminum
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Heater won't start automatically

I've got a Duo-Therm 65810-006 propane heater in my trailer, but I think my problem may not be specific to that model or brand. The problem is that it won't come on with the thermostat. The pilot light works fine and if I jump across the two wires at the thermostat the burner will light. But just turning the thermostat up to max (even on a cold morning) will not cause it to light. I tried replacing the thermostat, even though it appears to work electrically (the contacts close when they're supposed to and the resistance reads zero ohms). Still, I can't seem to get it to fire automatically the way it should. Any ideas?
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Old 09-22-2012, 01:53 PM   #2
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Hi Rick, welcome to FiberglassRV. Curiosity makes me ask... what brand of trailer? As far as the heater, see if any of the information in the Document Center will help you track down the problem:
Fiberglass RV - Document Center - Furnaces/Heaters

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Old 09-22-2012, 02:28 PM   #3
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Quote:
Originally Posted by RickU View Post
I've got a Duo-Therm 65810-006 propane heater in my trailer, but I think my problem may not be specific to that model or brand. The problem is that it won't come on with the thermostat. The pilot light works fine and if I jump across the two wires at the thermostat the burner will light. But just turning the thermostat up to max (even on a cold morning) will not cause it to light. I tried replacing the thermostat, even though it appears to work electrically (the contacts close when they're supposed to and the resistance reads zero ohms). Still, I can't seem to get it to fire automatically the way it should. Any ideas?
Measure the voltage across the two wires at the thermostat and watch what happens when you turn the thermostat up. The voltage be of some value, maybe 12 volts then drop to zero the the thermostat calls for heat.
On my thermostat there are two sets of contacts one that will not allow the heater to come on no matter where the temperature is set, the other that uses the temperature to determine on or off.
Sometimes that switch is a separate switch from the temperature control lever other times is part of the temperature control lever.

Good luck.
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Old 09-22-2012, 05:34 PM   #4
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I think that the "No Matter What Switch" is usually labeled ON/OFF, at least that's whats on several I have owned.
FWIW: If it starts when the wires at the thermostat are jumpered, it's gotta be the stat...

Although it may read OK on a meter, that may be a micro volt thermostat and the slightest amount of oxidation will stop it from working.
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Old 09-22-2012, 05:57 PM   #5
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Thermostats

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I think that the "No Matter What Switch" is usually labeled ON/OFF, at least that's whats on several I have owned.
FWIW: If it starts when the wires at the thermostat are jumpered, it's gotta be the stat...

Although it may read OK on a meter, that may be a micro volt thermostat and the slightest amount of oxidation will stop it from working.
Millivolt thermostats are not designed for 12 or 24 volt systems and 12 or 24 V thermostats are not designed for millivolt systems . If your furnace has a 12 or 24 V system make sure you set your thermostats anticipator correctly , if set incorrectly you can damage the thermostat or the furnace will not cycle properly . Mr Miller is correct if it works when you jumper the thermostat then the tstat is damaged or the tstat is incorrectly wired.
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Old 09-22-2012, 10:47 PM   #6
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The wires to the thermostat may be to blame. Measure the voltage at the terminals that you short to make it work, when they are not shorted. Are they the same terminals that the thermostat are connected to? Then the voltage at the thermostat should be the same. When the resistance drops to zero on the thermostat, is the resistance very nearly zero at the terminals that the thermostat connects to? This can be measured with a volt meter. If the resistance is zero, the voltage will also be zero between those points.
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Old 09-23-2012, 08:43 AM   #7
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Ohm Meter

Quote:
Originally Posted by RickU View Post
I've got a Duo-Therm 65810-006 propane heater in my trailer, but I think my problem may not be specific to that model or brand. The problem is that it won't come on with the thermostat. The pilot light works fine and if I jump across the two wires at the thermostat the burner will light. But just turning the thermostat up to max (even on a cold morning) will not cause it to light. I tried replacing the thermostat, even though it appears to work electrically (the contacts close when they're supposed to and the resistance reads zero ohms). Still, I can't seem to get it to fire automatically the way it should. Any ideas?
When testing with your ohm meter you are impressing battery voltage across the thermostat (Usually 9 volts) The thermostat resistance at 9 volts may be low but when impressed with millivoltage the resistance could be relatively high. Many times electrical components will read good with a meter but when put under load will not function properly. Relays and switches used with low voltage are often sealed and are specially designed for their application .
If you replaced the original millivoltage thermostat with one designed for 24v with heat anticipation the voltage drop across the anticipator will cause problems
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Old 09-23-2012, 07:06 PM   #8
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If the furnace lights when you cross the wires which attach to the thermostat and then the furnace does not light when the thermostat is installed there is a problem with the thermostat.
It's defective, installed improperly or it's not being operated properly.
Most thermostats have an on/off lever on the bottom.
Any inexpensive thermostat you buy at the hardware store should work with your heater right out of the package..

John
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Old 09-24-2012, 10:03 PM   #9
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Name: Rick
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Follow-up

Wow! What an embarrassment of help! You guys are really great! I was working on this on-and-off over the week-end, so líll respond to your questions and suggestions all at once.
Donna: The truth is Iím a fiberglass trailer owner wannabe. What I have now is an old steel and aluminum model. Itís a í73 Road Ranger. Nice enough for its age, but way too heavy. Now that we donít pull a horse trailer anymore, Iíd like to get rid of the horse trailer and replace that heavy travel trailer with something lighter (and newer) that I could pull with a smaller rig than my aging Suburban. Iíve just started looking into Fiberglass trailers.
Byron: I found out this is a millivolt system. The voltage measures about 275mV, then drops to virtually zero when the system is running.
Bob: The replacement thermostat does have an on/off switch, but it does not appear to force the heater on when in the ďonĒ position, it only prevents the heater from coming on when the switch is in the ďoffĒ position. Iíve verified that itís turned ďonĒ.
Steve: As noted above, mine is a mV system. The old thermostat was marked ďmillivolt systems only.Ē The new one says it will work with either, but the anticipator has to be set to ď1.2Ē. Iíve tried various settings on the anticipator, which will often trigger the furnace into running (when I change it). But no matter where I leave it, it wonít start automatically thereafter. Your point about the difference in resistance at 9V vs at 275mV is well taken.
David: Iíve shorted the system with the thermostat in place and with it temporarily removed. When the thermostat was in place, I jumped across the two screws that the wires were connected to. When the thermostat was removed, I connected to the two wires themselves. Since that works, I assume the wires themselves are ok (neither broken nor shorted somewhere else).
John: Ya, itís all leading to the same conclusion: bad thermostat. The old one looks original to the trailer. So maybe 35 years of clicking back and forth was just too much for it. The replacement one claimed it supported mV systems, but Iím suspicious about the system for adjusting the anticipator. Perhaps thatís not functioning properly (or Iím just not adjusting it correctly).
Conclusion: I picked up a new thermostat at Ace this eveningóone that has ďmillivoltĒ all over the packaging. J Iíll try to install it tomorrow and report back. Once again, many thanks to everyone who has contributed to this thread!
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Old 09-25-2012, 09:29 AM   #10
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From experience I have found that the lower cost thermostats do not function as well as a more expensive Honeywell T87 style stat. The less expensive ones are not as well built (sturdy) ,have flimsy anticipators and often cause large temperature swings (5 deg versus 1 1/2deg for a Honeywell) A few degrees does not seem like much but it is noticeable . Not to be sexist but women seem to be more sensitive to temperature variation then men .
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Old 09-27-2012, 06:41 PM   #11
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Name: Rick
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Fixed!

Well, the new $20 thermostat from Ace seems to have done it! I'm not surprised that the original one died after all of these years, but I sure was thrown off when the first replacement didn't fix it. In the end, I think the anticipator mechanism on that one didn't really like millivolt systems. Whatever the cause, the Ace one seems to work where the other one didn't. Now if I could just get the fan to shut off after the burner has been shut down for a while. I'm assuming that's just a broken internal thermostat of some sort. That's a problem I can live with for a while since this heater can be run with or without the fan (the fan was an optional feature for this model anyway, from what I've read).

Thanks so much to everyone who chipped in on this mystery! You guys are great!

--Rick
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Old 09-27-2012, 07:08 PM   #12
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I, and others are looking for that fan unit! Please post pictures of it! Pictures of your entire furnace, including closeups of the valve, and thermopile would be ideal. If not, please take a look at the following thread:
Trillium Furnaces - 9-3608 Blower

Is that your fan unit? If so, I will now be shopping for old Road Master trailers!
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Old 09-27-2012, 08:59 PM   #13
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Quote:
Originally Posted by David Tilston View Post
I, and others are looking for that fan unit! Please post pictures of it! Pictures of your entire furnace, including closeups of the valve, and thermopile would be ideal. If not, please take a look at the following thread:
Trillium Furnaces - 9-3608 Blower

Is that your fan unit? If so, I will now be shopping for old Road Master trailers!

Thermopile?????

FYI a thermopile is the temperature sensing part of an InfraRed thermometer.
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Old 09-27-2012, 10:59 PM   #14
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Name: Rick
Trailer: planning to move up from aluminum
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Fan unit

Duo-Therm 9.3608, that's the fella. The label with the model number is on the inside of the cover, just as in your photo. The trailer is a 1978 Kit Road Ranger (that's "RORAN" to the DOL). (I said '73 in my response to Donna, but that's the year of my boat--all these old vehicles of mine kind of run together in my memory. ) Do you still want me to upload photos or is that positive identification all you needed?

The trailer looks pretty stock in every other way, so I'd guess the fan was not added later. Which is to say, ya, start looking at 70's era Road Rangers and you might get lucky!

My fan is pretty noisy (could be bearings) and, as I say, once it's on it doesn't want to switch off automatically. But I'm guessing I can fix both of those issues when I pull it apart this winter.

--Rick
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