Suburban NT34 furnace ignitor works but does not light. + NT30SP idiots guide

[tiinytina]

Sent: 12/9/2005

We finally purchased our first RV a 1987 Tiffin Allegro 28' with a Suburban NT34 furnace. My problems are similar but the ignitor goes to town, the fans all come on.... the burner doesn't light. We have used compressed air and removed and blown out the propane input tubes. The water heater and stove work fine. We have a built in propane tank that reads half full at least. We were not, however parked on a level surface while doing all this know its important for fridge function but don't know if it is important for furnace function??? An additional problem with out unit though, is that the furnace is located half under the stove and the sink and the unit is too big to be removed through existing cabinetry. In fact, its downright difficult to get at, you have to work through 2 different cabinet doors...  I've surfed the Suburban site and its just full of warnings not to service the unit ourselves, which of course we are capable of doing. So far haven't found any diagrams etc or troubleshooting guides. The fridge doesn't work either but.... we knew that when we bought it, thats problem 2 to deal with after we pull and replace all the roof vents this weekend...
Thanks from a Newbie.....

[Slantsixness]

Sent: 12/9/2005

Tinytina,

Check out the message search in the sidebar option for fixing your fridge, search "burping" and you'll see what will likely fix the fridge, rather than buying a new one.

I have an NT36SE suburban, and I do believe it's similar. A lot of these furnaces are removed from the outside of the coach, behind the furnace vent. That may help you, too.

Tom

[tiinytina]

Sent: 12/9/2005

Tom,
    yes already downloaded all the "burping" info - this site rocks!
    The only access to the furnace from the outside is the intake and exhaust vent. I don't know if my hubby checked to see if there was anything blocking those... There is no "access door" to the furnace unless its underneath the siding...... Looks like the furnace was installed and the kitchen built around it.....
Thanx
Tina

[denisondc]

Sent: 12/9/2005

I don't know anything about the newer furnaces, that have igniter's, but...here is my guesswork...
I wouldn't assume the igniter was working unless I could see the spark it was making. It might click, but not produce a spark, or the spark be shorted out. So you couldn't be sure there was propane getting to the burner at all. Poking the flame from a hand held propane torch onto the burner as you turned on the furnace would be a better indicator of whether there was a burnable gas there. Don't do this if there is ANY smell of the propane gas (garlicky sentinel smell) of course. If possible you could loosen the compression fitting that connects the propane supply to the furnace, or to the all-purpose valve in the furnace; to see if propane was flowing. Of course, once you smell propane, then you have to quit for a while, let the propane disperse, and resume your investigation.
The main burner gas valve would be solenoid operated, probably with 12 volts on it to be open. You might be able to put a voltmeter on those terminals and see if that valve was being turned on.
There must be a safety scheme to prevent the gas from flowing indefinitely, in case the igniter doesnt work. I presume that would be a thermal sensor, and a control circuit/timer that would allow the burner to have gas flowing to it only for a limited period of time and while the igniter "clicked". This would involve electronics on a circuit board. And your RV being almost 20 years old -- I would suspect that circuit to be senile. If I had designed that circuit, I would certainly want to have it fail in the "gas off" condition.
So much for my guessing. 

[Easy]

Sent: 12/9/2005

You should have two coils to open the gas valve. One for the pilot and the other being the main.

After the unit has started, you should hear a click which would be the coils energizing and opening the valves. On mine, both valves open at the same time sending gas to the burner. My valve was opening and I could smell gas, but I had no ignition. I took the igniter out, cleaned it and the thermocouple, then replaced. I knew the igniter was working and I was smelling gas, but still couldn't get ignition.

I finally played around with the damper and wahlah, it fired off. The damper is adjusted by a small lever, usually located near the front of the unit, which regulates air flow going to the combustion chamber. May be something you want to try.

[enigma960080]

Sent: 12/10/2005

Just a  thought...  i was  having  issues  with my  refer  unit  lighting  while  on gas.   Sometimes  it would,  mostly  not.  Previous  owner  had  replaced  the  igniter  electrode  and  failed  to gap  it properly.  The  gap  was too small to  ignite  the  gas.
  I fooled  with the  spacing  until  it lit  on every  firing  run.
  I  thought  it worth a  shot... 
Good Luck

[Cooneytoones]

Sent: 12/11/2005

my guess would be if nothing is blocking the intake or out vent....it is the sail switch....it senses air movement when the fan comes on....if there is no air movement, the sail switch will not let gas flow through the gas valve, or the igniter's to get the 12v electrical current they need to work... if the sail switch is bad, or the connection to it is bad, same results will happen.

Timmy

[tiinytina]

Sent: 12/12/2005

Thanks for all the insight. And... once in a level place, it fired up just fine.... Guess it has to be level too. Need to buy a square socket to remove the fridge and start burping it, and after my mechanic crawled over the engine,,, a new carburetor is on order as well.... Thanks!
Tina

[tiinytina]

Sent: 12/8/2006

was laughing as I was the next to last post on this old thread.... but... the gremlin has returned.
On, now 2 occasions, we have parked Gone, pretty much level, and have attempted to start the furnace. Propane full, cleaned out wasp nests (buying a screeny thing next time I remember to), etc. On shore power furnace fans kick on, no ignition no heat. turn off repeat after 1-5 minutes... nothing... next day.. poof. heat. all works fine. Only thing we did was to remove the furnace cover so that we could see the ignitor, pilot etc. This past weekend I tried to start it at least 5-10 times over the course of 1-5 hrs. ended up on the oil filled electric radiator for the night and dog heat. Next morning... started up like a champ.
Our suburban  furnace has no access outside the Rv other than the input/output ducts. The unit sits under the oven and kitchen counter in between cabinets... so... we will essentially have to remove the entire kitchen lower cabinetry to remove the furnace. ( I love how engineers think in the "now" and not the "fix it later" realities...).

Tina

[Elandan2]

Sent: 12/9/2006

Tina, the "guts" of the furnace should slide out after disconnecting the gas line and the electrical plug.  There may be a couple screws holding it in.  After undoing everything, the unit should slide out into the motorhome.  Rick

[75Travco]

Sent: 12/9/2006

To add to Rick's post - the outside vent plates also have to be removed.  Then the "guts" of the funace can be slid out of the exterior casing.  If this funace has been in place for 20+ years, it certainly wouldn't hurt to remove it for a thorough cleaning and inspection.  No telling what you'll find - the problem may be very obvious once you have good access to the internals.  Unfortunately it sounds like you will have to perform some creative cutting and modification of the cabinets, but it may be possible to do this in a way so that the panels can be easily removed the next time.

[denisondc]

Sent: 12/9/2006

When you have access to things, you might want to remove/replace every electrical connector you find. If the problem is a bad/dirty/corroded connection, the movement in taking it off and putting it back will scrape it cleaner. Be careful you don't break anything on the circuit board of course.

[Easy]

Sent: 12/9/2006

The igniter boards in these units are somewhat fragile and with the bumps these things take going down the road and the extreme temperature differences they go through, they tend to go out from time to time.

I had one that would or would not work depending on how tight I tightened the screws on the outer housing. I knew it was a bad / broken circuit on the board, but I never found it. Sometimes it would work sometimes it wouldn't. I ended up buying a used heater and used the igniter board from the one I bought to put in my heater. Now with the newer board and my damper correctly adjusted, we stay nice and toasty.

Here's a link to some troubleshooting tips. http://www.dinosaurelectronics.com/Tips_Tricks_Page.htm

[tiinytina]

Sent: 12/14/2006

sorry for the long delay in responding.... biiiiizzzzzyyyyyy.
I'll take a pic next time I'm in her in the day time. Literally the furnace sits just to the right of a 14x9" door below the oven and under cabinet shelves under the sink.  Neither door is big enough to bring it out through.
Pat says its igniting each time we turn it on.... just not lighting.... then poof the next day it does. This is probably an issue to deal with for next year at this point but I'll look into the troubleshooting guides etc. 
Thanks for the suggestions.
Tina

[72leisuretime]

Sent: 12/15/2006

hi, could it be the safety switch that has to get hot enough for the burner to light.i had a problem with my furnace.it was a wire that is in front of the pilot light that goes back to the valve that controls the propane.all i had to do was push the wire probe closer to the pilot. mine has three options off/pilot only/on

[tiinytina]

Sent: 1/13/2007

hi all,
    pictures tomorrow I promise of our, have to remove the entire kitchen to get at furnace, "Gone"...  Here's a "blonde" question..... where the "he**" is the Sail switch? From looking under the 2 cabinet doors... I can see my ignitor. To the right of the ignitor are the, I'll say, coils, and on the right side of the 3 layers of coils are the "black box"... Wires in and wires out.
   Unless I remove my entire kitchen cabinetry, plus sink and stove, this unit is not coming out. There is no external access other than the intake/outtake pipes. Facing the kitchen the coach battery storage is directly to the right of the furnace with about 4" between them on the floor, directly under the sink. Furnace is under the couple of inches between the sink and stove and under the stove. 
   I can dig out all the coupling wires going into the furnace. I have the original furnace manuals and can probably decode some wiring...  Without removing the unit which I can't.... (OK I am looking for an excuse to rip out the kitchen and put in new counters and facing...) how can I test the sail switch, ignitor, and ignition board? I'm a plumbers daughter not an electrician... sorry for the "blonde" questions...
  And I promise pictures soon.
Tina

[pinballlarry1]

From: pinballlarry1
Sent: 1/14/2007

Curiously, I just worked on my spare Suburban NT12SE furnace that I purchased used from a guy in Oregon.  On the first try, the main blower would come on but no spark or gas valve.  Having the unit loose on the workbench made it easy to slide the guts out of the housing.  Beware of screws or rivets that obstruct the tight fitting sheet metal parts from sliding.  A flashlight around the edges is vital. 

After the internals were freed from the housing, a quick visual inspection showed that the sail switch was unable to spring back to the open position when the air fan shut down. The small micro-switch internal spring has become too weak to push the arm back when the air flow stops. 

I will replace the entire switch or just the micro switch depending on what I find on the Internet.  It's a standard Cherry long arm micro-switch used in hundreds of applications.  Anyway, I have discovered that unless the sail switch returns to the Open position, the controller board will lock out and not permit gas or spark.  The original Suburban board is a single shot, you only get 1 try with spark and gas for 10 seconds. If the flame is not detected, you get locked out, but the main fan will run until the thermostat is cycled.  Then you get another try, provided the sail switch is open, not closed.  Anything operating incorrectly causes a lockout, better for safety that way.  I believe that the newer Dinosaur circuit boards give you 3 tries before lockout and also shut off the main blower to save the battery. The sail switch on my NT12 unit is mounted on the rear of the burner chamber, directly in front of the blower fan blades, not visible until the unit is pulled all the way out. Once the sail switch was moved manually, everything worked great.

Lots of good information at Bryantrv.com, found the Suburban operating and troubleshooting manual at http://www.bryantrv.com/docs2/docs/ntseries.pdf
Will try to get photos soon.
pinballlarry

[tiinytina]

Sent: 1/14/2007

drat... I guess this problem will persist until we renovate the kitchen.... without a sawzall this unit is not moving..... I just love engineers and designers... I guess they never had to repair anything they ever built... oiy.
thanks for the advice!
Tina

[tiinytina]

Sent: 3/30/2007

After having to pull our entire kitchen out to get at and take out the furnace we thought we'd put a nice searchable post in about our adventures......

Our problem was that the furnace would work fine then only the fan would run and sometimes the ignitor would click... but no heat....

so.... (unless you are electrically inclined then you can check all this stuff with a meter but for the rest of us...)

1) check your intake/outtake... we didn't have a screeny thing and mud daubers and paper wasps had both built nests inside the fan area.... ours didn't restrict the air flow so the fan still kicked on full blast (ie. your thermostat still works). New screeny thing over inlet/outlet even though the manufacturer "Does not recommend doing so..." And yes for us it meant removing the entire unit and shaking it and using various tools to pull out the various nests... a lot of rust fell out as well which is probably a good thing.

2) if nothing happens.... 1 of 2 things to check first.... Thermostat itself...  and Ignitor board... we found our local Rv parts place will test your ignitor  board for free.... (ignitor board to replace was $140.. 2007). We didn't have to do a new thermostat so I wouldn't know what to check there.

3) if you can hear your ignitor clicking away at this point... your sail switch is working. (Sail switch was $12 on line) (Sail switch triggers ignitor to function)

4) if your ignitor isn't clicking.... yes new ignitor ($16 in 2007) plus new gasket probably ($10 2007)

5) check to see if you have gas getting to your furnace.... yes disconnect the gas line (turn the tank off)....

6) So fan is coming on, ignitor is clicking away.... no flame? Gas valve which in the case of the NT30 at least is all one unit with its accompanying solenoids....($101 in 2007).

7) Of course if your furnace is coming on fine but then shutting off... its the Limit switch....

In this case luckily the parts don't add up to a Whole new unit fortunately!.

so in summary...
The thermostat connected to the ignitor board
The ignitor board connected to the fan
Air flow connected to the Sail Switch
Sail switch also connected via ignitor board to the ignitor
ignitor connected  via ignitor board to the gas flow
Gas flow connected to the gas valve/solenoids....

and when it all works... poof! you have glorious heat!

Cheers
Tina and Pat and gone to the Dawgs... 

[bluebird]

Sent: 4/6/2007

SO ooo , did you get your furnace working?Huh? 

[tiinytina]

Sent: 4/9/2007

Yuppers! true test will be this coming weekend when we take her out for our first r and r weekend.
Tina 

[tiinytina]

Furnace has worked every time when needed....  if the gas has been turned off for a while turn it on and leave it on for a bit prior to trying to start the furnace. I always turn on and light a stove burner to make sure that the gas is indeed turned on and to allow it to fill the system if it has been off for a good bit.   Also installed a mud-dauber screen over inlet/outlet port outside RV... Sometimes it won't light first time turned on.. but in every case I've turned it back off, waited 5 min turned on, and houston we have heat!

Tina

[rnrphoto98]

The furnace on my 88 Elandan is right under my stove, It burnt the fuse the last time we used it and the fan makes noise so I am sure it needs a good cleaning.  Everything else seems to work ok.  What holds the furnace in place? 

It look like I will have to remove my oven and the plywood it sits on the get to the furnace.  Not a fun job, but if we want heat I dont have much of a choise.

Oh and any suggestions on taking out the stove?

Thanks

Rob

[tiinytina]

We had to take out the entire kitchen to work on our furnace... so been there did that.... unhook propane first.   think ours had a couple screws under burner cover into counter and a couple under it into bracing.... ours had the classic mud dauber leavings in the fan.. once cleaned otu all works great and put one of those screens over the intake/exhaust at all times.

Tina