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Old 07-22-2014, 08:00 AM   #1
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Suburban SF-20 Furnace Issue - ideas?

Good morning,

I have a new trailer with a Suburban SF-20 furnace. When I run it, I get the three attempts at lighting, and then it shuts down. The fan runs fine and blows cool air. Cool air coming from external exhaust as well. The dealer has already looked at it and was able to get it to run on 12v. I didn't see them light it, it was running when I got there, so I assumed all was fine.

1) I was able to smell some propane at the exhaust when I attempted to light
2) I'm able to light the stove
3) Propane tanks are full
4) Tried both 12v and shore power
5) Able to run AC and microwave on clean shore power at home. Also tried this at campground but not using that as a gold standard - just another test
6) My house is at ~6000 ft, dealer at ~5300 ft. Campground I also tried this at was ~5800 ft., so hopefully no altitude issues in play
7) I just tried this morning when it was ~66F outside, and I ran the AC to get interior down to 65F. I set t-stat at 85F and 90F just to get t-stat to kick heat on.
8) When I tried at the campground, and I first noticed it not working, I chalked it up to bad shore power because the microwave acted funny as well, and those campgrounds are not 100% reliable. I did not have surge protection and I did not try on 12v that time, so I assumed it was that shore power in that case. Microwave works fine on home shore power

Dealer has been very nice and is willing to continue helping me through this, so I'm not bagging on them. They explained they sometimes have difficulty testing these on very hot days and they bypass (hotwire) it to make it work - I assume at the limit switch. That's why I tried this morning with 66/67F outside and 65F inside. No luck. I haven't tried any limit switch hotwaire tricks myself because I'm not sure I know what I'm doing in that department.

I would think that's cool enough to get the heater to run as long as the t-stat setting was higher than internal temp and the t-stat would kick in.

Any similar experiences? Am I being unrealistic to expect it to work under these conditions?

Thank you for your time!
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Old 07-22-2014, 08:09 AM   #2
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The suburban sf-20 is a 12v only furnace so shore power is not an issue.
If IT'S clicking and the blower runs you've got power.
Try turning off tank valves and slooooowly turn them back on.
Light stove till your satisfied there's good flame.
It may take 5-6 starts to get the air out of the line.
It took me 25 minutes to get mine going this spring.

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Old 07-22-2014, 08:12 AM   #3
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Some thoughts-- 1st you are in warranty. Your dealer and not you should
be fixing this!!
2nd- Have someone turn on the furnace while you stand near BUT NOT
IN FRONT OF the outside exhaust. You will hear the fan start and then after a few seconds you should hear a snapping sound which
would be the board sparking the ignitor. The click is the spark jumping.
If you don't hear sparking sound each time the furnace tries to light it's
bad board or spark gap out of adjustment.
IF you do hear clicking AND smell gas but don't get ignition- I'm stumped.
Others will chime in I'm sure but again- this is a warranty job.
On all but the hottest day you should be able to turn your t-stat up to a
high number and the furnace should come on.
If the fan comes on- it should light.
If it doesn't it's warranty work.

Good luck!! I hope your dealer is close by!!
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Old 07-22-2014, 08:15 AM   #4
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https://www.google.com/url?sa=t&sour...71198958,d.b2U

Here's the pdf manual.

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Old 07-22-2014, 09:12 AM   #5
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Balky furnaces are a bear to troubleshoot, but you should get it going pretty quick.

Most common causes of your particular issue (blower running, Spark snapping, gas smell, but no ignition):

A) Low Propane Pressure - The heater requires MUCH more propane pressure than any other appliance in the camper. To test Propane pressure you need to put ALL your range burners on HIGH. The flames should be tall and blue. If low and yellow (or go out as you open other burners), the pigtail safety valve (designed to close in a fire or severed in an accident) has stuck in the closed position or has triggered because the bottle was opened too quickly (happens with NEW campers!).

1) CLOSE all propane bottles.

2) Rotate the bottle selector to the opposite tank you are about to open and SLOWLY (like try to take 30 seconds to crack the valve 1/4 turn). This will allow the gas to fill and pressurize the hose to the regulator.

3) Rotate the bottle selector SLOWLY to select the open bottle.

4) The GREEN indicator should show gas pressure.

5) Open ONE burner and light it. It may take a minute or so on high to flush out the lines to the range. Rotate the Piezo snapper until it lights. The flame should be tall and blue. Open the other burners and light them on HIGH too. ALL should be tall and blue and the regulator should stay green.

6) TURN OFF the HEATER and wait 30 seconds. (After 3 start attempts you must remove power top the furnace to try again).

7) Turn on the furnace. It should light right up within 6.8 seconds of blower blowing.

8) If not, after 3 attempts the furnace will shut down until you turn the thermostat to "OFF". Go to the next possible cause.

B) Mixture

Common causes of bad mixture (even in brand new units) are:

1) Loose screw in burner shutter causing shutter to vibrate open - too much air (mixture too lean)

2) Clogged Propane Jet - NEVER PROBE JET WITH PAPERCLIP - Examine jet visually for clean round hole. Dirt should be brushed away with an old toothbrush. (mixture too lean)

3) Clogged Burner Tube or flue - Blow out with compressed air - A bugs nest in the tube or in the flue can cause the initial burst of propane to fill the tube and not go up the flue. (Over-Rich mixture)

C) SPARK - If the gap is not according to the manual (1/8 inch), the spark may snap, but not be hot enough or in the right place for consistent ignition. It can also light and not stay lit. If the flame sensing circuit (uses ionization detection and NOT a thermocouple to detect if the flame lights). If the flame DOES light and goes out, the electrode or the control board will need to be replaced.
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Old 07-22-2014, 09:27 AM   #6
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***SOLVED***

Thanks, all, for your help with this. It was frustrating for sure. A couple people suggested the idea of turning propane off/slowly on and trying again. In fact, in the manual I was given, it mentions this as well. I made the assumption (stupidly), that since the stove and fridge would run fine on propane and since the dealer had it working somehow when I showed up, there was no leak protection valve triggered and nothing to do with propane flow, so I thought turning the propane on/off was not my issue. I was wrong. I'm going to follow these steps from the beginning from now on.

Here's what I did, and what folks are basically recommending in this thread:
1) Turn off propane
2) Burn off propane in the lines with the stove
3) Run cycle of furnace (knowing it won't light, but clearing any propane in that line when attempting to light three times). Then turn off thermostat
4) Slowly (VERY SLOWLY) turn on tanks and make sure selector is on a tank which is full. They're both full, so that's easy in this case
5) Turn on stove for a couple minutes to get propane back in line and consistent flow
6) Turn on furnace

Result: First clicks didn't work, but probably because it needed a solid flow of propane in that line. Then, on second clicks, SUCCESS! That beautiful sound of gas igniting - in a controlled, expected sort of way. Hot air out the exhaust immediately, and hot air from the vents. Let it run several minutes. Shut it off. When fan stopped, I fired it up again and it ignitied the first try.

So, all is good. Thank you so much for the information and time helping me walk through this.
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Old 07-22-2014, 02:11 PM   #7
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We love a happy ending!
And thanks for telling us "the rest of the story"!

Happy Trails!
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Old 07-22-2014, 02:51 PM   #8
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Hey! Sounds good!
Glad we could help!
Glad you now have heat!
Fyi IT'S 99 DEGREES real feel here today!
I think the a/c is running overtime!
Have fun!

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Old 07-27-2014, 07:52 PM   #9
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***UNSOLVED***

Alright, so I thought I had it solved when I got the heater to light as I state in my ***SOLVED*** post above.

We just got back from a trip to the mountains where the temps at night were ~55F. Interior was down to 58F or so at times. I could not get the heater to light once. I tried the steps above, except those which might require removing the furnace to check screws/valves/mixture issues. I also tried another propane bottle (3 total) - all were probably at least 75%-100% full. I do have the auto-switch propane splitter and tried slowly turning/selecting the tanks. It shows green and I slowly opened the tanks. 12v batteries were full (I had a generator to recharge them as well).

I'll be calling the dealer tomorrow to discuss, but it must be something a qualified technician needs to dig into, right? I think I've tried everything I can do without removing the unit and doing more technical adjustment and troubleshooting.

Thanks again for your help.
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