Suburban SF-30 furnace lights then goes out

[PoppySteve]

I have been doing a bit of research on this problem and think I have it narrowed down to a few things.

The problem is that I can hear the furnace burner lighting then shuts off about 2 seconds later. It does this the normal 3 times.

My reading seems to points to some solutions. Low gas pressure, faulty flame sensor, control board.

I am thinking the easiest thing to do first is replace the LP regulator and see if that helps. If it has not been replaced in the past, it's about 10 years old.

What do you think? Is this a waste of time and money? Should I just move onto looking at the flame sensor/control board? I hear that board could be $130.

I guess I could just buy a Mr. Buddy

[PoppySteve]

After some more looking around, the flame sensor function is built on the control board and uses the igniter. This seems to now point to low gas pressure or faulty control board.

I am not sure it's worth the $$ to try and fix. We generally stay in electric sites and run space heaters.

[SeaDog]

you might want to test the sail switch. If the other appliances that use propane are not experiencing problems I doubt its the regulator

[5picker]

Originally Posted by SeaDog

you might want to test the sail switch. If the other appliances that use propane are not experiencing problems I doubt its the regulator

The OP says the furnace lights, then goes out.
If the sail switch was bad, the furnace would never even attempt to light.

With that said, I did have a bad switch-over regulator on my current R/V and while the furnace lit, it never really got hot. Replacing the regulator fixed that. Turned out, it was one of the little check valves on the regulator end of the pigtail to the tank. I found out later the check valve was available separately but I replaced the entire regulator with a higher BTU rated one anyway for just a few $$ more. That ended my issues.

I never experienced any issues with the fridge, oven, stove, or water heater, only the furnace. It is a propane hog and need LOTS of LP.

[Larry-NC]

Originally Posted by SeaDog

you might want to test the sail switch. If the other appliances that use propane are not experiencing problems I doubt its the regulator

If the sail switch were faulty, the heater wouldn't even attempt to light. The OP states that the heater repeatedly makes three attempts to light.

His statement was that it lights and immediately goes out. I'm interpreting it to mean that the gas in the chamber ignites (he hears "whoomp") but combustion is not sustained.

This is almost always due to a faulty regulator. The regulator lifetime is about 8-12 years. His is 10 years old. The SF-series of Suburban furnaces is very sensitive to gas pressure--much more so than the range, refrigerator, or water heater.

There is one other item to check first: Make sure that mud dauber wasps have not built a nest in the intake or exhaust vents on the exterior of the RV.

[PoppySteve]

Thanks Larry, your post was a good summation of what I am experiencing. The intake and exhaust vents are clear.

Your statement - " I'm interpreting it to mean that the gas in the chamber ignites (he hears "whoomp") but combustion is not sustained. " is very accurate.

I think a new regulator would be the first start and I will see how it goes.

Thanks for all the feedback.

[Thomas ho]

tap top of heater box several times. and turn on furnace, repeat if it doesnt work . FIXED MINE.

[Larry-NC]

Originally Posted by PoppySteve

Thanks Larry, your post was a good summation of what I am experiencing. The intake and exhaust vents are clear.

Your statement - " I'm interpreting it to mean that the gas in the chamber ignites (he hears "whoomp") but combustion is not sustained. " is very accurate.

I think a new regulator would be the first start and I will see how it goes.

Thanks for all the feedback.

New regulators are readily available on Amazon and probably eBay. There are two things to watch.

Your regulator is either Horizontal or Vertical. The new one must be the same as the old one. (When you look at pictures on Amazon, you will see the difference.

Some regulators have two inward ports (for RVs with two tanks) and some have one. The new one must be the same as the old one. I don't know which type your RV uses. Once again, looking at yours and looking at the online pictures will make the decision easy.

[Scrapper]

Originally Posted by PoppySteve

After some more looking around, the flame sensor function is built on the control board and uses the igniter. This seems to now point to low gas pressure or faulty control board.

I am not sure it's worth the $$ to try and fix. We generally stay in electric sites and run space heaters.

Check the position of the igniter/flame sensor. If it is just outside of specs it could cause the same symptoms. When the burner lights the igniter/flame sensor sends a micro voltage back to the control board.


See page 29 of the attached service manual.


4. Burner ignites, but goes off and into lockout:
a. Check to be certain that flame sensor is over slots in the main
burner and that the main burner flame is burning against the tip
of the flame sensor - adjust by bending sensor probe. NOTE:
Sensor probe should be in the inner blue cone of the burner
flame (approximately 1/4" t o 5/16" above burner).
b. Burner still goes off and into lockout - check wire connections
at flame sensor and at module board.
c. Wire connections OK - check continuity through flame sensor
wire.
d. Continuity of flame sensor wire OK - check with micro amp
meter in series with flame sensor and flame sensor wire to be
certain that the flame sensor is generating at least seven
micro amps within seven seconds after the burner is ignited.
Connect meter as follows: (+) to sensor wire, (-) to sensor
probe. Adjust position of sensor probe, check for carbon
deposits on sensor probe if reading is less than seven micro
amps.
e. Flame sensor circuit generating at least seven micro amps,
but burner still goes off and into lockout - replace module
board.
5. Repeated module

[TheWolfPaq82]

Make sure the "Flame Sensor" is in DIRECT CONTACT with the flame. It may ignite, but if it's not DIRECTLY in the path, it won't sense the flame and trip the gas valve.

[Rekab]

Originally Posted by 5picker

The OP says the furnace lights, then goes out.
If the sail switch was bad, the furnace would never even attempt to light.

With that said, I did have a bad switch-over regulator on my current R/V and while the furnace lit, it never really got hot. Replacing the regulator fixed that. Turned out, it was one of the little check valves on the regulator end of the pigtail to the tank. I found out later the check valve was available separately but I replaced the entire regulator with a higher BTU rated one anyway for just a few $$ more. That ended my issues.

I never experienced any issues with the fridge, oven, stove, or water heater, only the furnace. It is a propane hog and need LOTS of LP.

Additional question since I am having the same issue. Is the regulator in question on or near the tank or on the furnace? My furnace has no outside access so I have to remove from under the fridge to see anything.

[Larry-NC]

Originally Posted by Rekab

Additional question since I am having the same issue. Is the regulator in question on or near the tank or on the furnace? My furnace has no outside access so I have to remove from under the fridge to see anything.

Rekab, since you have neither described your RV in your signature line nor put it in your profile, it's a difficult question to answer.

• If you have a pull-behind trailer with one portable tank near the hitch, it will be near the tank.
• If you have a pull-behind trailer with two portable tanks near the hitch, it will be on the hold-down clamp that holds the two tanks in place.
• If you have a 5th Wheel trailer, it will be near the tank.
• If you have a motorhome it will also be near the tank and probably be a one-port horizontal regulator.

[Rekab]

Sorry about that. I have a Forest River Lexington GTS. Thanks for your response

[PoppySteve]

Thanks for the info on the ignitor/flame sensor position. If the regulator does not do the job, and at 10 years old it's probably worth replacing anyway, then the next step I suppose would be to pull the unit and make the adjustment. There is a good video online for that procedure.

https://www.youtube.com/watch?app=desktop&v=uGVN1xws4Tw

For clarity, I have a 2011 Sunseeker 2860 with built-in (I guess you might say) LP tank.

And I want to thank everyone for their help. There are a lot of good folks on this site.

[PoppySteve]

Purchased and installed a Mr. Heater F273863. Furnace fired right up and has been cycling on/off for a couple of hours now.

I know diddly squat about propane regulators, but this one looked different, came with the POL and regulator covers.

FYI, I saw one brand that was rated for 9 WC instead of 11.
Thanks all

[Scrapper]

Originally Posted by PoppySteve

Purchased and installed a Mr. Heater F273863. Furnace fired right up and has been cycling on/off for a couple of hours now.

I know diddly squat about propane regulators, but this one looked different, came with the POL and regulator covers.

FYI, I saw one brand that was rated for 9 WC instead of 11.
Thanks all

LP gas appliances use 11"WC. I believe the 9"WC is for natural gas fired bar-b-cue and fire pits.