heater trouble

[fltioga898]

hi folks, I just bought a used class c yesterday and im having trouble getting the heater to stay lit. this is a 1996 suburban unit. it tries and tries to start burning but it wont stay going, it just sparks and lights then goes out and sparks again and lights and goes out. this will continue if I don't turn it off .
any suggestions on where to start, also access to it is going to be very difficult, I don't know why it doesn't have an access panel from the outside like the refrigs do. thanks

[Harvey51]

Thanks for the maintenance tips, old biscuit. I have copied them for future use.

[efiguero]

Thanks for the suggestions, it's at our storage area now but when I go out there I'll get the model info.

[Old-Biscuit]

efiguero wrote:
Hey I'm having almost the exact situation in my 97 Tioga Class C, except mine just cycles twice then gives up. It lights, stays lit for about a minute or less, then goes out, it lights again for a minute then goes out and stops cycling. If I go to the outside access door and flip the switch out there it seems to reset and does the same two cycles again with the same results. During all this, the blower in the furnace is running fine but just blowing cold air since the the flame keeps going out. In reading some of the comments in this thread, are you guys saying I can remove the furnace and clean it?

That switch in your outside access is a slow blow style CB/On-Off switch.

If you are having to reset it i norder for furnace to do a relight then you have a motor/circuit problem. That switch being slow blow type has to see excessive amp draw over a period of time to trip.
Could be low DC voltage issue causing high amp draw, could be really dirty blower/combustion wheels causing motor drag or could be motor going bad.

Yes you can pull furnaces to clean them..course depending on furnace some are easier than others.

Google your Brand & model for manual.....or post what you have.

[Bordercollie]

In addition to the above, make sure that the 12 volt positive and ground connections to the furnace are making good contact and that furnace is getting over 12 volts DC. If you can unplug the PC board, clean it's contacts and plug it back in. You may be getting air bubbles in the propane line. Try running the stove top and water heater for some minutes then the furnace. There are some troubleshooting videos on You Tube.

[efiguero]

Hey I'm having almost the exact situation in my 97 Tioga Class C, except mine just cycles twice then gives up. It lights, stays lit for about a minute or less, then goes out, it lights again for a minute then goes out and stops cycling. If I go to the outside access door and flip the switch out there it seems to reset and does the same two cycles again with the same results. During all this, the blower in the furnace is running fine but just blowing cold air since the the flame keeps going out. In reading some of the comments in this thread, are you guys saying I can remove the furnace and clean it?

[Old-Biscuit]

ronfisherman wrote:

Old-Biscuit wrote:
It being a Suburban in a Class C it can only be accessed from inside.

I believe the Tioga can be assessed from the outside.

OP stated it was a Suburban in a 1996 Class C that was just purchased..nothing about a Tioga. And that it didn't have an outside access

[APRSRVer]

As Old-Bisciut says, flame sense is done by electrodes in flame plasma and is small signal back to control board. So try to clean contacts at the board by working connector on and off a few times and and using something on board and connector contacts. Description of trouble seems to indicate everything is working but control doesn't know flame exists. This has worked for me on several occasions. HW heaters also.

[fltioga898]

thanks for all the replies, I guess im going to pull it out and really go over it. I don't have a tioga anymore , this one is a born free . I might be able to crawl into the cargo area which is under the bed and get to the burner area of the unit, but it will definitely be tight.

[Teacher_s_Pet]

We had a Suburban years ago that did that, found it had a hole in the heat exchanger after buying and replacing sensors, switches and boards. Remedy was a new furnace. Sometimes it pays to let a good RV technician look at it. In our case we ended up with a bunch of extra "new parts" we never needed.

[ronfisherman]

Old-Biscuit wrote:
It being a Suburban in a Class C it can only be accessed from inside.

I believe the Tioga can be assessed from the outside.

[Old-Biscuit]

It being a Suburban in a Class C it can only be accessed from inside.

Could be dirty burner/burner chamber
Could be faulty spark electrode (the electrode is used to prove main flame...milivot signal generated by main flame goes back to control board via electrode to prove flame and hold gas valve open)
Could be low gas pressure

Could be low DC voltage.

The 'sail switch' is making up otherwise the spark electrode would not get power to spark nor would gas valve get power to open. Sail Switch has to make up before any of that can occur.
Low DC voltage could cause motor to slow down when spark electrode/gas valve get power causing sail switch to drop out which then would have to make back up sending power to board.....

Most likely problem is that it's a 1996 and is dirty due to having to remove furnace completely in order to clean it out.....which probably has not been done.

Start with the easy basic.....pull furnace and clean up the blower & combustion wheels, clean out the burner assembly, clean the gas orifice (unscrew & clean with alcohol), clean off spark electrode with emery cloth, clean out the combustion chamber & clean the connector contacts on board with pencil eraser.

Probably lots of rust/dirt

[John_S2]

When I had this problem the sail switch had to be replaced.

[j-d]

This Link to Service Manuals might be of help.

The furnace has a way to "prove flame" which means that it feels for heat and shuts down if heat not found. It also looks for air flow which typically is what they call a "sail switch."

Sometimes there's outside access to the furnace, other times not. Ours does not have outside access either.

'Nuff for theory. An easy first step would be see what you can do to make sure the two tubes to the outside of the coach are clear of critter nests. We've seen cases where there was a nest IN the squirrel cage blower inside the furnace. That's going to reduce air flow and shut it down on sail switch.