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Old 01-16-2019, 08:28 AM   #1
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Furnace doesn't kick back on

The furnace in my camper will kick on and work perfectly 2 or 3 times and then it won't run again until you turn it off and then back on with the thermostat. The furnace is a suburban sf35f. I've replaced the thermostat and the control box in the ceiling. Any ideas? I'm thinking the module board.
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Old 01-16-2019, 08:31 AM   #2
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The furnace in my camper will kick on and work perfectly 2 or 3 times and then it won't run again until you turn it off and then back on with the thermostat. The furnace is a suburban sf35f. I've replaced the thermostat and the control box in the ceiling. Any ideas? I'm thinking the module board.
I would look at the time delay relay if it has one they seem to be chincy.
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Old 01-16-2019, 11:20 AM   #3
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The SF35F doesn't have the time delay relay, that's handled in the control module.

We've had the same symptoms you describe several times and it's usually the control module in the furnace that's the problem.
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Old 01-16-2019, 11:32 AM   #4
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The SF35F doesn't have the time delay relay, that's handled in the control module.

We've had the same symptoms you describe several times and it's usually the control module in the furnace that's the problem.
Agreed. I've experienced the same.
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Old 01-16-2019, 03:19 PM   #5
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Furnace

Yep, had same thing and was the furnace panel. Replaced under warranty and problem solved
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Old 01-16-2019, 05:33 PM   #6
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Not always the controller board

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Originally Posted by Bama Rambler View Post
The SF35F doesn't have the time delay relay, that's handled in the control module.

We've had the same symptoms you describe several times and it's usually the control module in the furnace that's the problem.
You can also have the "failure to ignite" which requires the "reset by off/on" caused by a pressure regulator that's going bad. I'm referring to the gadget that's connected to the propane tank(s). If the regulator is more than a few years old, that's a definite possibility. The water heater and range are pretty insensitive to propane pressure, but the Suburban furnace is very fussy.

Ask me how I know.

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Old 01-16-2019, 06:12 PM   #7
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If under warranty have the dealer replace with suburban made control board. If it is not go to amazon and get a dinosaur brand control board much better made product.

Hope this helps Tim
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Old 01-16-2019, 07:01 PM   #8
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Overstuffed wallets?

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If under warranty have the dealer replace with suburban made control board. If it is not go to amazon and get a dinosaur brand control board much better made product.

Hope this helps Tim
You guys must have overstuffed wallets if you recommend replacing the control board without doing a little bit of troubleshooting. To start with, all you need is your ears.

There are several reasons that the furnace will fail to light on three attempts and go into "lockout." The control board is only one of them, and (IMHO) not the most likely.
  1. Furnace clogged with dust. Suburban recommends not using a filter (any obstruction) so the whole area gets clogged with dust. If there's not enough airflow, the "sail switch" will not close and the furnace won't even attempt to light. (I can envision people removing the furnace, cleaning everything, replacing a perfectly good control board, having the furnace work, and attributing the fix to the control board when it really was the cleaning.)
  2. Bad propane regulator. This happened to me. The furnace was reliable with the plenum cover off, would light every time. Put the cover on and it wouldn't light. I checked gap, spark, sail switch, high limit switch, and everything else. All was in order. Even though the Suburban manual tells you to check gas pressure FIRST, I had put it off because I had no gauge. Finally I took some scrap wood, spare Romex staples, and $3 of fittings from Lowes and built a gauge. Sure enough, the 14-year-old regulator was bad. Next time it will be the first thing I check.

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Old 01-16-2019, 09:38 PM   #9
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Thanks for all the input, I did go ahead and order a new dinosaur board from Amazon so we'll see if this fixes it. Btw the regulator is new, had to put a new one on after I got this camper because the previous owner had it hooked to a residential propane tank so it has new regulator and hoses.
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Old 01-16-2019, 09:55 PM   #10
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Take off the grille

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Thanks for all the input, I did go ahead and order a new dinosaur board from Amazon so we'll see if this fixes it. Btw the regulator is new, had to put a new one on after I got this camper because the previous owner had it hooked to a residential propane tank so it has new regulator and hoses.
To install the new board, you will first have to
  • Take off the grille: Probably four Robertson screws. You will be amazed at all the dust and gunk behind it. You might as well get out the vacuum and start cleaning as you go. There will be more.
  • Turn off the gas on all tanks. Then disconnect the gas line at the furnace.
  • There will be four wires going into the furnace. If there's a connector, unplug it. If not, the wires will be long enough to remove the furnace and work on it in place.
  • Remove the furnace front plenum cover. It's the only thing you can see. Probably one sheet metal screw at the top edge.
  • Vacuum some more.
  • At this point you could actually reassemble the furnace and see if cleaning it fixed it.
  • If not, remove the furnace anchor screw at the front bottom center, approximately just below where you removed the plenum cover screw.
  • Pull the furnace out. Vacuum some more.
  • At the back you will see the double-ended fan motor, two squirrel-cage blowers, and the control board. Vacuum the squirrel-cage blowers, then clean them with an old toothbrush, then vacuum again.
  • Change the controller board if you are really convinced that it's a problem.
  • With the furnace out, you will see the two tubes exiting outside for the firebox intake and exhaust. They should be perfectly clean. If not, clean them. Vacuum some more. It's not unusual for mud daubers to nest there and clog the tubes with mud, hard to get out.
  • Now the tricky part: If you are really good, you will be able to slide the furnace back into the plenum, engaging the two tubes from the firebox onto the two vent tubes. It's hard. If you cannot do it, you will have to remove the vent from the outside. After the furnace is back together, you will have to put the vent back on with new butyl tape.
  • Reconnect the wires and the gas line before putting the anchor screw in.
  • Install the plenum cover and grille.
  • Re-install the vent cover if you had to take it off.

Larry
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