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Old 01-12-2019, 02:20 PM   #1
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Suburban SF-35FQ won't light

I have a 2015 ATC with the aforementioned furnace in it. On a recent trip the unit failed to ignite. I have searched all over and performed various troubleshooting and I'm thoroughly stumped...and confused.

Symptoms: Place T-stat into heat mode and furnace blower starts. After about 10 seconds I hear the gas valve click and the igniter sparking. It tries to ignite 3 times, then times out. I do NOT smell any propane during this process.

Troubleshooting steps: I have removed the furnace for bench testing and have failed so far. I have tried multiple times to bleed the lines as well as "choke start" by covering the air intake. I have also tried a shorter gas line whip off my bbq direct to a fresh tank, all to no avail. I thought the gas valve at the furnace might be the issue. I can hear it make a loud click when it tries to ignite. I have tested across the coil leads on the valve and I get 40ohms on both coils. I think this is good.
My control board doesn't appear to be equipped with any lights so I can't use those to help troubleshoot.

I have also verified that I have 12-13 volts at the control board.

To this point I feel like I don't know what to check next. I haven't been able to locate a test procedure for the control board or the gas valve. Any help would be appreciated. Otherwise I'm to the point of either hiring someone to take a look or just start throwing new parts at it.
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Old 01-12-2019, 04:19 PM   #2
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Quote:
Originally Posted by wellsit View Post
I have a 2015 ATC with the aforementioned furnace in it. On a recent trip the unit failed to ignite. I have searched all over and performed various troubleshooting and I'm thoroughly stumped...and confused.

Symptoms: Place T-stat into heat mode and furnace blower starts. After about 10 seconds I hear the gas valve click and the igniter sparking. It tries to ignite 3 times, then times out. I do NOT smell any propane during this process.

Troubleshooting steps: I have removed the furnace for bench testing and have failed so far. I have tried multiple times to bleed the lines as well as "choke start" by covering the air intake. I have also tried a shorter gas line whip off my bbq direct to a fresh tank, all to no avail. I thought the gas valve at the furnace might be the issue. I can hear it make a loud click when it tries to ignite. I have tested across the coil leads on the valve and I get 40ohms on both coils. I think this is good.
My control board doesn't appear to be equipped with any lights so I can't use those to help troubleshoot.

I have also verified that I have 12-13 volts at the control board.

To this point I feel like I don't know what to check next. I haven't been able to locate a test procedure for the control board or the gas valve. Any help would be appreciated. Otherwise I'm to the point of either hiring someone to take a look or just start throwing new parts at it.
My experience relates to an Atwood, but here goes.

If you are truly hearing the electric spark/arc, then the only thing left is gas (unless it briefly lights, and a faulty flame sensor shuts it down). Is there air in the line? Is the rig gas pressure evidently good at the stove? You can build a DIY manometer (google it) for about $10 to measure the gas pressure at the furnace (but you will need a fitting for the port). You say that you hear the gas valve solenoid operate, but as you know, there are two. Maybe one is stuck (long-shot)?
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Old 01-12-2019, 04:21 PM   #3
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Im having an issue with my heater too that I just posted today.

Ive also spent about an hour on "YOU TUBE" under RV Furnace troubleshooting. I THINK I may have a circuit board problem. Mine doesn't even start the fan or click. From what you are describing and from what I watched on YOU TUBE.....maybe a bad "sail switch". Apparently when the fan starts, there is a little paddle(sail switch) that the fan moves with the air flow after reaching a certain RPM that then sends signal to a "limit switch" that then allows power to the circuit board and the gas valve.

Pretty good video. You tube RV Heating System Overview and Troubleshooting. Two techs explaining the system (ABC's OF RV's). Im going to do some tests on mine after watching this. Good luck with yours.
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Old 01-12-2019, 04:26 PM   #4
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Does the stove light? It sounds like it is cycling. Do you have insect screens over the furnace outlet.. Dirt daubers like to go in protected openings and make dirt nests. This will disrupt the airflow and cause it not to light.
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Old 01-12-2019, 04:39 PM   #5
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Quote:
Originally Posted by Det57 View Post
Im having an issue with my heater too that I just posted today.

Ive also spent about an hour on "YOU TUBE" under RV Furnace troubleshooting. I THINK I may have a circuit board problem. Mine doesn't even start the fan or click. From what you are describing and from what I watched on YOU TUBE.....maybe a bad "sail switch". Apparently when the fan starts, there is a little paddle(sail switch) that the fan moves with the air flow after reaching a certain RPM that then sends signal to a "limit switch" that then allows power to the circuit board and the gas valve.

Pretty good video. You tube RV Heating System Overview and Troubleshooting. Two techs explaining the system (ABC's OF RV's). Im going to do some tests on mine after watching this. Good luck with yours.
It has been over twenty years since I went to school on the furnace, but if I remember correctly, the sail switch must close for the igniter to spark and the gas valve to open. Since you are hearing this, your sail switch is O.K.
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Old 01-12-2019, 06:16 PM   #6
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Thanks for all of the replies, I really appreciate it.
It is my understanding that the sail switch is good because the igniter is attempting to light...like GA traveler said.
I don't see any evidence of bugs in the system. I have removed the cover over the igniter and verified spark. No other debris was evident.
I'll thinking that because I can't smell propane, it must be a gas issue. I've tried a different gas hose and regulator but no joy.
Is there a voltage check at the gas valve?
I'm thinking my problem is either with the circuit board or the gas valve but don't know how to go about testing.
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Old 01-12-2019, 06:18 PM   #7
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Oh yeah, forgot to say that yes, the stove, oven and fridge all run on propane just fine.
The burner doesn't ignite at all. Not even briefly.
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Old 01-12-2019, 08:08 PM   #8
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Found this from a service manual:

3.Electrode sparking and gas valve opening, but burner will
not light:
a.Check to see if gas is coming through to the burner.
This can be accomplished by using a flow meter in the
gas supply line. If no gas is coming through the burner,
check for obstruction in gas line, in main burner orifice,
or in main burner.
b.Gas is coming through burner, but spark will still not
ignite burner - check gas pressure.
Line Pressure - Min. 11 W.C.*, Max. 14 W.C.
To properly check pressure, first determine the line
pressure, cycle furnace and check pressure drop on
demand. The drop in pressure should not be more than
W.C. A drop of more than 1/2 W.C. would indicate a
faulty regulator, a restriction in the gas line, or a pinched
gas line. Excessive pressure drop could also be due to
moisture contamination.
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Old 01-12-2019, 09:42 PM   #9
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Ok, thanks for that info 1982. I guess I'll need to figure out a way to measure the line pressure.
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Old 01-12-2019, 11:45 PM   #10
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Had same problem in W Yellowstone last May. Mobile tech came and adjusted the spark gap to a wider than spec setting. Think I remember he set to 3/16" or close to 1/4". Stronger spark!! Just like setting the spark plug gap on gas engines wider for a "hotter" spark back when!! Another thing he did was "aim" electrode to spark right at the holes that let gas up into the electrode area!! It was aimed off center, to use a term, not hitting the gas holes well. Starts on first try usually (without air in lines!!), hasn't failed to light since.

Need to have a couple of gaskets and a "bent" wrench for gas line to remove the cover over the igniter. Sure you could find from a RV tech in your area.
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Old 01-13-2019, 12:08 AM   #11
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furnace

i would check the gas oraface i have seen them pluged with muddaber nest to check the electrical check for 12v applyed to valve coils when ignitor is clicking
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Old 01-13-2019, 12:16 AM   #12
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As mentioned....spark electrode MUST be centered over burner slots and the gap must be set correctly

OEM gap is 1/8"
(See PAGE 3 in LINK Below)



Both solenoids MUST operate for gas valve to open and allow flow thru it
40 ohms is normal


http://docs.renegaderv.com/Suburban/...11-08-2013.pdf
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Old 01-13-2019, 02:08 AM   #13
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That troubleshooting guide looks like it should be useful.
I tried checking voltage at the valve but the meter was showing very sporadic readings.
On the valve, there are 4 terminals. It looks like terminals 1 & 3 should be positive and 2 & 4 should be negative. Can someone verify?
I should be able to just place my multi meter on the terminals for each coil and get a voltage reading right?
What does it mean if my measurements are all over the place? They jump around so much that I can't tell what it should be.
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Old 01-13-2019, 12:01 PM   #14
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Voltmeter set to DC Voltage
Voltmeter probes on each solenoid terminals ......when circuit board sends DC to gas valve (will only be on each solenoid for 6-8 seconds when spark electrode is 'clicking')


From wiring diagram terminals 1 & 2 are on one solenoid & terminals 3 & 4 on other solenoid
DC from circuit board goes to terminals 1 & 4 (Brown wires)

Terminals 2 & 3 go to ground (Yellow wires)
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