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I have a 2002 toybox trailer with a Atwood 8500-IV furnace.

When I turn on thermostat...
I have a 2002 toybox trailer with a Atwood 8500-IV furnace. When I turn on thermostat and raise setting furnace blower starts up but the burner does not light up. all other trailer burners work fine, stove fridge,water heater. propane is full, I tried switching tanks. Blew everything out, bled the gas line. I had similar issue two years ago replaced thermostat did not help, I believe it was a moisture problem because a couple days later it started working. last time i used it was sevral months ago and all was fine.
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Answered in 14 minutes by:
4/14/2013
RV Mechanic: Randall, RVIA Certification replied 9 years ago
Randall
Randall, RVIA Certification
Category: RV
Satisfied Customers: 28,176
Experience: RVDA/RVIA Master Certified Technician with many years experience.
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Hi: Thank you for coming to Just Answer with your question. My name is XXXXX XXXXX perhaps I can assist you with this issue.

The two most common causes of this are low LP pressure at the tank regulator and a bad control board. Low DC input voltage can cause this as well if it is below 11 VDC at the furnace. This will have a separate timed delay relay and if this is still the OEM board it is about time for a new one. Most won't go this long. I would use an after market board made by Dinosaur Electronics as they are far superior to the OEM boards and have an outstanding warranty should you ever need it. Most dealers stock these. If you have an outside inspection cover you can open it up and remove the board and take it in for testing. Once you remove the wing nut it just unplugs. Try those things first and then get back to me if we need to go further here.

Hope that proves helpful. Please get back to me if you need more as all follow ups are included in our fee. No limit as to time or number of responses needed.
Randall
Randall, RVIA Certification
Category: RV
Satisfied Customers: 28,176
Experience: RVDA/RVIA Master Certified Technician with many years experience.
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Randall and 87 other RV Specialists are ready to help you
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Customer reply replied 9 years ago

I will give it a try the board makes sense to me hopefully the local shop will have something in stock


thanks for the quick reply


 


mike

RV Mechanic: Randall, RVIA Certification replied 9 years ago
You are welcome, Mike.............go and CLICK HERE for a copy of the Atwood Service Manual which covers this unit. Lots of good information in there. Bookmark it so you can come back to it again any time.

Thanks for the great rating...........and please tell your friends about our service here at Just Answer!
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Customer reply replied 9 years ago

well i jut got to a camping world got a new board put it on and no change still will not light up all other lp utilities are workig fine any ideas

RV Mechanic: Randall, RVIA Certification replied 9 years ago
Do you have a 12 VDC test light so we can track the current though the unit? About $5 at most automotive or hardware stores. That way I can have you do some checking and we can sort this out.
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Customer reply replied 9 years ago

well last it worked but i just stoped in el reno ok because we are in very bad rain storm and it wont come on im sure because its wet i will have to wait till its dry which may be a couple days i will get back to u thanks for the reply

RV Mechanic: Randall, RVIA Certification replied 9 years ago
O.K...........pick up a 12 VDC test light and we can check this out and get to the bottom of the problem quickly.
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Customer reply replied 9 years ago

well i finally have time and its not raining. a few days ago i turned it on and it worked then when temp got right it turned off as it sould but would not ome back on then it did not come on at all for a few days, the blower did not even work. now last night i turned it on a it worked but again when temp was reached it shut off and would not come on again. any ideas i have a test light i will check back on email often today thanks again


mike

RV Mechanic: Randall, RVIA Certification replied 9 years ago
That is usually one of two things. Either the blue leads to the thermostat got reversed OR you have some ducts closed or some debris in there that is holding the heat into the furnace and it is cycling on the limit switch. Did you or anyone have the furnace out or the thermostat disconnected? You mentioned replacing it several years ago. What is the style of thermostat you have? Both heat and cool or just heat only? Mechanical, analog or digital? I have seen them wired up wrong at the factory, but that is pretty rare.

Check the ducts and be sure they are all open and that there is no debris in there from mice or kids or trash from the floor.

And did you have the LP pressure at the tank regulator checked? If that is too low it will cause the furnace to overheat and can trip out the limit switch. OR the limit switch may be defective.

OR just a bad connection can do this. The way to track this down is to eliminate as many of the above as you can first. THEN, start up the furnace and allow it to cycle. When it won't come back on you take your test light and find out if there is power to the board or not. Was the new one an OEM board or a Dinosaur Electronics board? Does it have the timed delay ON the board or separately as shown in the manual. IF the relay is separate, then test for power INTO it from the thermostat FIRST. IF the motor won't come back on it has to be in the relay OR the thermostat OR board USUALLY.

See what you can find, Mike and we can go from there...........
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Customer reply replied 9 years ago

ok i checked ducts all good, two years ago i out on new thermostat it did nit make a difference then a few days later when things dried out it worked and has since then i jst out old one back on no change.



thermostat is for heat and aur and is mechanical new board is oem


i did not check lp regulator


i think the time delay s on the board


what is the limit switch


i keep thinking it has to do with the lp


 


 


the closet rv shop is an hour away i will get there on friday and get new valve and what ever else ya think


 


thanks again mike


 


h.

RV Mechanic: Randall, RVIA Certification replied 9 years ago
I think you need to be sure that the leads to the thermostat didn't get swapped around. I would always use a Dinosaur Electronics board instead of an OEM board as those are too unreliable. Have the LP pressure at the tank regulator checked or perhaps just buy a new one. Those aren't that expensive and neither are thermostats. I believe I would swap out the leads in that just to see if that is the problem.
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