Furnace doesn't kick back on

[Natesev]

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.

[ejohnson1144]

Originally Posted by Natesev

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.

[Bama Rambler]

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.

[5picker]

Originally Posted by Bama Rambler

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.

[jrmorris]

Yep, had same thing and was the furnace panel. Replaced under warranty and problem solved

[Larry-NC]

Originally Posted by Bama Rambler

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.

Larry

[TimVWulp]

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

[Larry-NC]

Originally Posted by TimVWulp

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.

Larry

[Natesev]

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.

[Larry-NC]

Originally Posted by Natesev

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

[TimVWulp]

Forest River Forums - Downloads - Furnace - Suburban Operation (Various models)

I atached a link from the library at the the top of this page to work on suburban furnaces. There is a lot of information in the library on how to fix and maintain your RV.

Hope this helps Tim

[Natesev]

I put the new board in the other day and it seems to have fixed the problem, it has been replaced before so we'll see. Thanks for all the help

[Larry-NC]

Originally Posted by Natesev

I put the new board in the other day and it seems to have fixed the problem, it has been replaced before so we'll see. Thanks for all the help

So how dirty was it inside? Did you clean it much?

Larry

[Natesev]

It actually wasn't dirty believe it or not, I did have the vacuum on stand by figuring it would need a little but it was good

[Natesev]

Originally Posted by TimVWulp

Forest River Forums - Downloads - Furnace - Suburban Operation (Various models)

I atached a link from the library at the the top of this page to work on suburban furnaces. There is a lot of information in the library on how to fix and maintain your RV.

Hope this helps Tim

That is very handy thank you

[Larry-NC]

Originally Posted by Natesev

It actually wasn't dirty believe it or not, I did have the vacuum on stand by figuring it would need a little but it was good

To be honest, my experience has been limited to a trailer in which a very hairy, shedding dog resides.

Larry

[Natesev]

Ok so the new board seemed to work for a while but now it's being dumb again, it works fine sometimes but not at all other times. I did notice when changing out the thermostat that came with the new relay box that the was a couple other wires not being used which leads me to believe this trailer had an analog thermostat. Any other ideas?

[Bama Rambler]

What happens if you connect the thermostat wires at the furnace together while it's acting up, Does it work correctly then?

You could always add a furnace only thermostat somewhere.

[Natesev]

I will give this a try

[TimVWulp]

Originally Posted by Natesev

Ok so the new board seemed to work for a while but now it's being dumb again, it works fine sometimes but not at all other times. I did notice when changing out the thermostat that came with the new relay box that the was a couple other wires not being used which leads me to believe this trailer had an analog thermostat. Any other ideas?

Hi sorry to hear that you are still having trouble. The furnace has 2 wires that go to the thermostat. At the thermostat they are generally red and white. The red wire is connected to the R terminal and white is on the W Terminal. R or red is 12 volts + and white or W is the 12 volts + back to the furnace to start it. Do not short across the R and W terminals as this may cause a short and burn out the heat anticipator resistor in the thermostat. Remove the wires from R and W on the thermostat and put them together. The furnace should start and fire up as long as they are together. I have seen several post where the thermostat switch was going bad or failed. When this happens the furnace will not start the furnace fan or go into lock out failure mode.

hope this helps Tim