Suburban Furnace Problems

Check the feather switch. It controls the gas valve and must be proved before you get gas.

and you have to have a good 12volt source. meny a times all thats wrong is the battery is low,even when plugged into shore power.

"Feather" switch? Do you mean the sail switch?
Clean the unit good.
Check all the electrical connections.
Inspect the ignitor/flame sensor probe. Look for crack in the procilan.
Inspect the contacts on the thermostat. Look for pitting.

Check the air in/exhaust ports too. Bees and spiders love to make nests in them.

JeffRil wrote:
So my dad gave me his old rv that he just replaced the main board in the furnace its a Suburban model NT34 S and it seems to run fine about 3 time, then it goes to ignite the 4th time and will not ignite, fan runs, and there is spark but no fire, I have taken it apart and cleaned it all and re-thread taped all the gas lines, it is getting propane because it runs the other 3 times just fine but then wont start unless I turn the thermostat completely off and then back on again.

If anyone has any ideas or any way to point me I would really appreciate it, Thank you in advance.

Explain HOW you know it runs 3 times. How much time difference between each time it runs? IF it sparks but there is NO flame. Assuming you have a OLD NT 34 S. Odds are you have a defective Gas Valve. It is sticking. If it Sparks, the control electronics and switches WORK. That means the Sail switch and Hi limit switch function to spec. What I do when I get this model and it fails to light but DOES spark is, I hit the galvanized gas elbow where it goes into the furnace with a hammer when it sparks. That will usually make the sticking gas valve open up and then I know it is a bad gas valve. What you experiance is exactly what a sticking gas valve will allow to happen. Doug

Ernest wrote:
Check the feather switch. It controls the gas valve and must be proved before you get gas.

If it sparks the "feather"(SAIL) switch is functioning. Doug

I have taken it fully apart and cleaned everything, I made sure all connections where fully connected and that all wires where in working order and that all intake and output vents where free of anything, the sail switch works just fine also, I tested it, when I checked the wiring, it was a bit dusty but i cleaned it off.

And Doug I know it is lighting because I have the main from panel off of it that is held on by just two screws, and just above where the igniter is mounted in is a viewing window, I have watched the flames light three times and then the fourth time nothing, it runs until it reaches the temp the thermostat is set too, then it turns off and when it gets cold enough it turns back on, like it is suppose too but that fourth time nothing.

I will try hitting the elbow where the gas goes into the furnace before the valve a few times to see if it lights a fourth time, I will do this a few different times and get back with you about the outcome.

If it is the valve is there a way to service the valve to make it work? I`m strapped for cash at the moment.

Sounds like it could be the thermostat. Is this the small 2.5 inch square variety?

enblethen wrote:
Sounds like it could be the thermostat. Is this the small 2.5 inch square variety?

If it sparks, or the fan comes on, the Tstat has nothing to do with that part of operation. ALL the tstat does, is send a 12 volt signal to the furnace to start a heating sequence, nothing else. Doug

JeffRil wrote:
I have taken it fully apart and cleaned everything, I made sure all connections where fully connected and that all wires where in working order and that all intake and output vents where free of anything, the sail switch works just fine also, I tested it, when I checked the wiring, it was a bit dusty but i cleaned it off.

And Doug I know it is lighting because I have the main from panel off of it that is held on by just two screws, and just above where the igniter is mounted in is a viewing window, I have watched the flames light three times and then the fourth time nothing, it runs until it reaches the temp the thermostat is set too, then it turns off and when it gets cold enough it turns back on, like it is suppose too but that fourth time nothing.

I will try hitting the elbow where the gas goes into the furnace before the valve a few times to see if it lights a fourth time, I will do this a few different times and get back with you about the outcome.

If it is the valve is there a way to service the valve to make it work? I`m strapped for cash at the moment.

GAS valves are dual solenoid and are NOT serviceable. Replacement is the ONLY option. Doug