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Old 12-05-2014, 10:52 AM   #15
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No I am not mistaken. The principle involved is called flame rectification. Google it and see how it works. The flame rod is a conductor. You are confusing the older thermocouples with a flame rod. Thermocouples such as you find on older furnaces and hot water tanks did indeed generate their own power by being heated because of two different metals. The newer Atwood and Suburban furnaces that have a circuit board use the flame rectification method where the flame sensor is a conductor not a voltage generator.


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Old 12-05-2014, 01:34 PM   #16
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It's been about three weeks since the original post, I'd just like to know if they got it fixed and what was wrong with it.
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Old 12-26-2014, 08:30 PM   #17
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Update : It is the main RV furnace and its a Suburban brand, SFV -35 Q. We have had unit at an authorized Suburban dealer, they have replaced the board and the limit switch, still not fixed. Their thoughts are, there is a ductwork issue that is causing the unit to go into 'lockout' after one cycle. Still frustrated :/
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Old 12-26-2014, 09:15 PM   #18
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They should be able to pull the unit out of the rv and bench test it. All it needs to bench test it is propane and twelve volt power. Removing the furnace isn't that big of a shore.
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Old 12-27-2014, 10:09 AM   #19
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The dealer said it bench tests fine.
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Old 12-27-2014, 10:33 AM   #20
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Can you make it run in fan only mode?

Get an old computer fan or just use a lighter to observe air flow from the ductwork.

If there is a kink in it behind something the air flow will be too low and may be your problem.

If newish and dealer still has one you can compare flow to theirs.
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Old 12-27-2014, 09:53 PM   #21
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If I go to thermostat and turn off for 5-10 seconds, then turn it back on, it works perfect for one cycle. But then it will not restart on its own.
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Old 12-28-2014, 08:43 AM   #22
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Quote:
Originally Posted by Bella222 View Post
If I go to thermostat and turn off for 5-10 seconds, then turn it back on, it works perfect for one cycle. But then it will not restart on its own.
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My 40,000 BTU Suberban SF-42F propane furnace has a similar problem.

After it has not been used for 2-3 days it will not fire the first time the thermostat is turned on, (it only blows cold).
If I allow it to blow cold for 5 minutes, then turn the thermostat OFF and ON again, the furnace blows, fires and heats until the cabin temperature reaches the thermostat set point.
Then it cycles on/off normally ... (but only for 1 or 2 cycles).
After that if/when the cabin temp drops below the thermostat set point, (or if the thermostat is turned up) the blower comes on but the burner refuses to fire.
If I turn the thermostat OFF after the furnace has been "blowing cold" for 5 minutes, and turn it back ON... it will blow, fire and heat normally for another cycle or 2.... but then it once again refuses to fire when the cabin temperature drops below the thermostat set point.
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Old 12-28-2014, 11:20 AM   #23
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Jim is right, a flame will conduct current. Modern devices use this method to confirm ignition.

OP, call Heartland and get them involved. Also, join the Heartland Owners Forum, lots of fine folks and free advice. Also, Heartland is active in forum and will help you. This should be a simple problem to fix. Good luck.
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Old 12-29-2014, 05:47 PM   #24
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Just to update a little. Hubby is in the belly working and found a crimped area in the ducting . And found a place where the hole was drilled only partially, allowing a reduced amount of air to flow. He is still working on it now, so stayed tuned ......

Thx for all the help !
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Old 12-29-2014, 05:50 PM   #25
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Heartland has been involved. They nearly got it back !!!! Pray for patience .
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Old 12-29-2014, 06:34 PM   #26
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Had that problem with my Atwood for several years, In 2012 it quit working on gas completly, a new Control board fixed it and I've not had that problem since.

That said I do not often run it on gas,, Last time was. The Sunday before Christmas,, Got home from darling Daughters went to shave and shower and found I'd left the thing off.. So turned on both switches for a fast heat up.. Had a nice shower about half an hour later.

I fund the problem only happened (in my case) on cold starts. Once the water was warm it worked,, Leads me to think moisture.
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Old 12-30-2014, 01:14 AM   #27
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On the Suburban sf-35 when the heater fires and it is really cold, before the t-stat temp is met and the over temp snap switch opens ( high fire box temp), the gas valve closes. The fan keeps running. When fire box cools the hi temp snap switch closes. The gas valves opens again and heating resumes. This cycle goes on for 5 cycles. If T-stat temp is not reached with in the 5 cycles, the board shuts the gas valve down for 1 hour. (Timer is built into the board) You wake up and the damn heater is blowing cold air. The way to reset the 5 cycle safety is to remove all 12 volt from the heater and reconnect it. (I use the fuse to do that) ( NOW) Suburban says there is not enough air flow through the ducts if the snap switch opens. (BS) I have had my heater snap switch cycle when every duct connection on my heater was removed on a 50f day with wind blowing around the heater. I replaced my snap switch and finally installed a smaller main jet. All new 4 inch ducting and it will still cycle if it is really cold. 18f This is why people go nuts trying to work on these heaters and most techs do not know about the cycling. I use a Dinosaur board and they confirm that this is the way they work
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Old 01-02-2015, 01:13 PM   #28
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Well its not working again.
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