RV Furnace

[Rather B Fishing]

Looking for help and advice with a Suburban SF25 furnace.  Problem is intermittent which is the worst kind.  The furnace will run for about 20 seconds, there is no ignition spark and then shut down.  Sometimes it works just fine, others not.  No particular pattern.  I suspect it is the sail switch and/or control board so thinking about replacing both.  I have found a tune up kit on line but there are 2 versions.  The first (Kit #1) has the old style burner access gasket which makes kit #1 applicable to the SF-25F between serial numbers 934701426 and 094101431, the second (Kit #2) has the new style burner access gasket which is applicable to the SF-25F above serial number 094101431.  I suspect that I need the older model because the furnace is in a 2004 trailer.  To get at the plate where the serial number is would require removing the furnace and my RV is permanently parked at a seasonal site at Tomahawk Resort in Sioux Narrows Ontario (a place that I would highly recommend) so taking it in to a repair shop isn't really an option.  I do have a qualified repair person who will do on site work but that can get pricey too.  Airxcel, the parent company for Suburban, has yet to reply to any of my previous questions so I have pretty much given up on them.  Any insights as to what kit I need, who I might contact to determine which kit or any other ideas about my problem woud be greatly appreciated.

[Kirk W]

Since you are permanently parked, it should be safe to believe that your 12V supply to the furnace is solid, but just to make sure you should use a good digital meter and verify the power at the furnace is above 11V while the problem is happening. Low voltage will cause the blower motor to run slower and that, in turn, will prevent the sail switch from closing. It is common to have that problem with RVs when without 120V shore-power, but you should not have that issue. Since you are probably depending on a converter for 12V, it could be a problem so you should check that first.

Your furnace has an igniter probe that can fail as can the ignition circuit board. For any part, you should get the serial number of your furnace because if you do not, you will risk getting the wrong version of that part. There is also another option available to you in that you could remove the furnace and take it to an RV repair shop. Most of the shops do have temporary 12V and propane supplies for working on the furnace on the bench. To do serious troubleshooting of your version of a Suburban furnace it is almost required.

[oldjohnt]

  On some RV furnaces (maybe NOT yours, check manual linked below) if the T stat calls for heat it sends power to the control board and the fan starts and then (if alls well) the sail switch closes (if voltage sufficient and resultant adequate air flow, INSURE GOOD VOLTAGE IS PRESENT) then the gas valve opens (possible to hear and/or feel it) and the HV igniter starts firing (clik clik clik snap snap snap). If it doesn't ignite it shuts down.

A few among a ton of possibilities Ive often seen (On some RV furnaces maybe not yours) are faulty ignitor tip (hairline crack or carbon trace or shorted),,,,,,,,,,ignitor tip not proper gap and location to burner,,,,,,,,,,,,,,,,,,,,,,,bad ignition HV cable,,,,,,,,,,,,,,,,,,,bad control circuit board,,,,,,,,,,,,,,bad ignitor control (some ignitor controls are small separate mounted units).

 I would download the manual and follow its troubleshooting NOT mine. Before I replace the board I would insure its getting good voltage,,,,,,,the HV coil on the board or if separate is producing the HV,,,,,,,,,,,,,,,,,,,,if so the boards likely okay so its simply an ignitor tip problem (crack or short or carbon trace or mis located or bad cable), if not (NO HV) then I suspect the board. On some boards with the HV coil readily available I use a jumper wire from its HV terminal to ground to see if it jumps a spark there ?? If so the board is good so its an ignitor tip issue. if not and there's good voltage then I suspect the board. A new ignitor tip often comes with a new HV cable attached, that has cured many similar failure to ignite issues for me. If a whole new board is in order, I like to use Dinosaur Electronics units.

 You gotta have gas present at the furnace ya know WELL DUH   KISS  Check for Gas and check voltage and look for the board producing a HV spark !!!!!! Does it matter if plugged to shore power or not ????????????? 

Star with a manual and its troubleshooting and a good voltage check,,,,,,,,,,,,see if gas valve opens and HV fires,,,,,,,,,,,,

 https://www.manualslib.com/products/Suburban-Sf-25-3550350.html

Nuff for now, late for church lol

Best wishes n God Bless

John T

 

[Wrknrvr]

 If you pull your suburban furnace out to work on it make absolutely make shore you apply propane trough a regulator and twelve volt power to test it before and after you install new parts. Putting the two blue wires should turn the furnace on when they are put together .

 

 Now from my experience I will say it maybe a ground problem where the burner assembly screws tight to the burn chamber. But as you know you must pull it out to work on it in your situation . After your first test for operation I would remove the burn chamber and inspect it. To remove the burn chamber you will need a 5/8" crows foot wrench and an extension to remove the propane line from the gas valve. Cheap harbor freight tool will work for this.Then sand all contact points where the burn chamber assembly is screwed to the burn chamber. I know it is stainless but just use my experience on this.

 

 My first time I discovered that problem the customer did not want to pay for my time. He said I did nothing to fix it. So if I see a furnace with your situation I absolutely state that it may just be a ground issue for the spark probe to sense spark .

 

 Now by testing before and after each possible fix, test it for operation .  

 

With inflation I will it's my three cents of info,.   Vern

[Kirk W]

I forgot to post the link for you to get a copy of the service manual for the furnace.

      Bryant RV Service ~ Suburban SF-25

[Wrknrvr]

 If I remember correctly my procedure for testing flame sense and the ground problem is not in that manual.

 

 That's 4 cents now,.   Vern

[oldjohnt]

48 minutes ago, Wrknrvr said:

If I remember correctly my procedure for testing flame sense and the ground problem is not in that manual.

Vern, the manuals don't go into a lot of detail grrrrrrrrrrrrrrrr

In the Suburban SF 25 Manual I posted above:  https://www.manualslib.com/products/Suburban-Sf-25-3550350.html

On Page 27 Troubleshooting:  https://www.manualslib.com/manual/799721/Suburban-Dd-17dsi.html?page=27#manual

NOTE the manual seems to cover different models so no warranty its the correct one although on the first link it states Suburban SF 25 ??

It simply states "Check ground wire on terminal block"

If its NOT sensing flame it shuts down, but is that because a) There is no flame b) Bad Ground c) Bad circuit board or connector see Note 2 below  d) low voltage etc etc

While the board may be bad, I try cheap easy simple things first like low voltage or bad ground (Check all connections, especially including the frame ground screw) or a relatively cheaper (then new board) ignitor tip (when board is producing the HV snap snap snap) before I move on to a new board.

Note 2 I have had furnaces act that way which were cured SIMPLY by removing the flat ribbon cable (on furnaces that use such to the board) and using a pencil eraser to lightly gently clean/buff/polish the brass looking flat contacts on the board, replace the connector THEY WERE FIXED yayyyyyyyyyyyyyyyy  I even cured one where the board was producing the HV but it still didn't ignite the gas SIMPLY by adjusting the ignition tip ever so slightly to the correct distance (fairly critical, check manual)  away from the burner...……….  

Good luck let us know what you find, these are NOT all the possibilities, check the manual troubleshooting.

John T

[Kirk W]

1 hour ago, Wrknrvr said:

 If I remember correctly my procedure for testing flame sense and the ground problem is not in that manual.

You do remember correctly. Like most RV related service manuals, there is very little about troubleshooting techniques. 

[Dutch_12078]

My first "test" anytime I work on an RV furnace, water heater, or fridge "fails to light or stay lit" problem, is to simply clean the wiring connection contacts at the igniter board. The flame sense circuit works in the millivolt range, so it takes very little contact corrosion to disrupt it. Even just removing and reinserting the connector a few times will sometimes be enough to get it to fire up correctly.

[bags]

the furnace Is 14v years old. Stuff wears out. Ours died at 13 years with 10 inches of snow on the ground. Same symptoms as yours .  Ours would start in the morning and not turn on again. Best 5 0r 6 hundred dollars I have spent in a while.

Good luck

JB

[oldjohnt]

11 hours ago, Dutch_12078 said:

is to simply clean the wiring connection contacts at the igniter board.

Yo Dutch, that's very similar to the fix I noted above. On the boards that have the flat ribbon cable that connects to the board I remove the connector, use a pencil eraser to lightly clean/polish the boards brass looking flat contact strips, maybe when in there check any ground screw/terminal  (remove clean and replace maybe a new shiny screw), check voltage, check (maybe remove clean n replace) any other connections OFTEN GOOD TO GO after that and ZERO cost yayyyyyyyyyy lol.

 While I've had to replace circuit boards and/or igniters on several older RV gas appliances, I've seen more of those as the cause versus simply blaming it on "old age". Good regular routine maintenance goes a long way...…...

John T

[Kirk W]

11 hours ago, Dutch_12078 said:

Even just removing and reinserting the connector a few times will sometimes be enough to get it to fire up correctly.

I would agree with that, especially since this trailer just sits in one place and doesn't travel. While that means no vibration to cause damage it also makes it more susceptible to dirt and corrosion. His problem is that he has one of the older versions of Suburban furnace that has no outside access like an Atwood and the newer Suburbans do, which means his can only be accessed from the inside and to do that means removing the furnace from the RV because the builder put it inside one of the cabinets. I learned about those early Suburban furnaces the hard way. You just don't have access to troubleshoot without pulling them out of the RV. You can connect 12V and troubleshoot pretty much everything except ignition on the bench but most of us do not have a means of supplying propane except with it installed in the RV. 

RATHER B FISHING , it would be nice if you would let us know what is happening as it seems that you have not signed into the forums since you made that first post. We are happy to help if we can.

[oldjohnt]

 Rather B Fishing, FYI I successfully repaired a Suburban SF 25 about a year or so ago in a 2006 RV that failed to ignite. On that one (but maybe NOT yours ???) all I had to do to get to "some" of the furnace for preliminary troubleshooting (voltage, some connections, grounds etc) solely from the outside, was remove the four hex head screws and pull the outside sheet metal cover (where air intake and exhaust is which MUST be outside) out/off, easy piece of cake. It's possible (or at least that one was) to check ground terminal/screw/connections and some of the electricals and voltage and the board is "somewhat" accessible from the outside simply with the outer cover removed. On that unit the board was mounted sideways and NOT as easy to get to if it was flat facing you grrrrrrrrrrrrrrrr.  HOWEVER if you need to get to the igniter tip that's more difficult. I had to remove the gas line and furnace body screws and ducts so I was able to slide it out far enough to work on, but still NOT all the way out.

  For a beginner Id say if you cant troubleshoot the easy simple things like voltage and grounds perhaps a few accessible connections which can be done simply by removing the four screws and outside sheet metal cover, it may be best to hire a professional, but if you want to tackle it that's your choice.

 DISCLAIMER I've slept since I made that repair and my recollection may not be exact, but best I recall I was able to access and troubleshoot some (not all) all from the outside simply by removing the four screws and outside cover BUT NO WARRANTY YOUR RV MAY BE FAR DIFFERENT !!!!!!!!!!!!!

Best wishes, God Bless and good luck

John T

[Rather B Fishing]

The quality of the information that my questions has generated is amazing.  I have a few updates on the issues that I have been having over the weekend.  The furnace continued to work intermittently but then there was a change in what is going on.  After one of the 30 second fan runs but not spark cycles I gave the furnace a couple of light taps with my hand to see if that changed anything.  It did but not in a good way.  Now when I turn the furnace on the fan runs, there is no ignition spark but the fan just keeps running.  When I try to turn it off at the themostat it just keeps running.  I ended up having to pull the 15 amp fuse to shut it down.  Didn't try disconnecting the wires at the themostat which I probably should have just to take the themostat out of the loop as the source of the problem.  It was 2 Celsius on Sunday morning with a vicious north wind and it was "shut down weekend" for us.  We may indeed be at the point of getting a new furnace but have some time to make that decision.  I am going to pass along all of the suggestions that have been made on this forum to the company that we have been using to work on our RV.  I tested the voltage from the converter and it was OK.  The hot water tank fires just fine even with a stove burner going so I think that the regulator is providing sufficient pressure.  I switched propane tanks just to make sure that wasn't a factor.  Thank you to everyone who has been so generous with their time and expertise.

[oldjohnt]

Rather B, THANKS for the update. FYI on "some" RV furnaces if ignition fails for whatever reason, the gas valve closes and it stops trying to ignite BUT THE FAN CONTINUES TO RUN ON. On "some" later models orrrrrrrrrrrrrrr ones that have an updated control board (like some of the Dinosaur replacement boards) if there's ignition failure the fan runs for a short purge period but then shuts down. Anytime I had to replace a circuit board when possible I used one with the fan shut down option in case of no fire so the fan didn't keep running and drain the battery.

Looks like you're back to square one with possible bad/loose/resistive connections or a loose/resistive ground or an ignitor tip failure or sail switch failure or finally a bad board (see all the tips above). The last SF 25 I worked on ended up an ignitor tip problem instead of a more expensive new board.

Thanks again, best wishes

John T

[Kirk W]

3 hours ago, Rather B Fishing said:

Didn't try disconnecting the wires at the themostat which I probably should have just to take the themostat out of the loop as the source of the problem. 

You probably would not have gained anything if you had removed it since turning it off didn't help as turning it off does the same thing as the thermostat does when a temperature is reached, just opening the connection between the two thermostat leads(blue leads in the furnace). When the thermostat closes the blower should start and run for about 30 seconds when the gas valve is supposed to open and the igniter should try 3 times. If it does not detect heat from combustion after 3 attempts, it should close the gas valve and go into lockout. Some models leave the blower running and others shut it down after a couple of minutes. 

[oldjohnt]

6 hours ago, Rather B Fishing said:

I probably should have just to take the themostat out of the loop as the source of the problem

Rather B Fishing, I apologize, I didn't address that specific portion of your post in my answer above MY BAD. Between prepping the RV for heading out again, moving into to a new home, and finishing up and closing a couple law clients probate actions, I've been busier then a one armed paper hanger lol.  Actually, I don't think the thermostat is the source of your problem (may be never say never) as it must be closing and calling for heat which starts the fan and hopefully the sail switch engages and the ignition process starts (open gas valve and fire the HV ignitor) so that part works right??  That being said, in the event you might require a new circuit board (still my last resort AFTER voltage and grounds and connections and ignitor tip have alllllllllllll first been eliminated as the problem) see if its possible to get one with the feature that shuts down the fan in the event of no flame. The last of such type I bought came from Dinosaur Electronics.

Thanks again for the updates

Best wishes

John T

[Rather B Fishing]

Thought I might provide an update for those who have been kind enough to provide me with some advice and guidance.  It has been a long cold winter here with no end in sight.  Took in the RV show in Winnipeg Manitoba this weekend and after not finding a new RV that meets our needs we have decided to follow the advice previously provided by Bags and get a new furnace.  It will likely be pricey enough with installation as is the case with most RV stuff but it is after all a 14 year old furnace.  Pretty sure that it will be less than the $35,000 that the new trailers were going for.  My parents gave me their 2004 Salem 28FKSS  four years ago when they weren't able to use it any longer. They had also had some furnace issues.  I have something of a sentimental attachment to it and in general it meets our needs.  Had the hot water tank replaced last year, put a new battery on it, replaced the bathroom fan, new set of kitchen taps and that has been about it.  Have to say that I am pretty impressed with the quality of the information that was provided to me and I really do appreciate the willingness to share.

[Kirk W]

5 hours ago, Rather B Fishing said:

Thought I might provide an update

Thank you for taking the time to update us. We tend to wonder what the end result was when people don't bother to let us know.