Suburban Furnace Question: Not igniting

[LY007]

My new to me 83 Excella has an NT-30 M furnace. When I turn the switch on at the thermostat, the fan starts up and a few seconds I hear one click which I think is the solenoid opening. All good. But then I never hear any electrode clicks. I replaced the electrode but I don't hear it and of course all I get is cold air. Any thoughts? And shouldn't the unit shut itself down if it's not making heat?

The stove works fine so I assume I have adequate gas pressure.


Also, if I find it cheaper to replace than repair, will an NT-30 SP model line up with the existing vents?

Steve

[HowieE]

That is common when there is air in the line. If a tank was off the trailer and the regulator open to that tank air will get in the line. The stove has enough flow to purge itself but the heater does not.

What I do is crack the gas line at the heater just till you smell gas and retry.

[cameront120]

What Howie said. It can sometimes take a while for the gas to reach the appliance.

[LY007]

Ok thanks will try that tomorrow.

Steve

[Gearheart]

Did the 83 have an igniter? My 73 only has a pilot light.

[woodfox45]

Originally Posted by LY007

My new to me 83 Excella has an NT-30 M furnace. When I turn the switch on at the thermostat, the fan starts up and a few seconds I hear one click which I think is the solenoid opening. All good. But then I never hear any electrode clicks. I replaced the electrode but I don't hear it and of course all I get is cold air. Any thoughts? And shouldn't the unit shut itself down if it's not making heat?

The stove works fine so I assume I have adequate gas pressure.


Also, if I find it cheaper to replace than repair, will an NT-30 SP model line up with the existing vents?

Steve

I'm not trying to be a smart A@@ is the gas valve turned on ?

[Chatooga11]

low battery power can cause the same symptoms. That was my issue when my 86 did the same thing.

[LY007]

Gas valve on. Battery voltage 13.2.

[woodfox45]

The instructions on my 85 were as follows with gas valve off turn on thermostat and let blower run for 5 minutes shut off ,turn on gas valve and turn thermostat back on for ignition .

[Richard Pope]

It's been a long time since I have had my Suburban out of the trailer for inspection but I do remember after experiencing the fan running a long time without ignition that there was a "flapper" or "damper" inside that got stuck because of sitting so long. I released it and lubed it and it worked. When it fell into correct position, it opened the valves to start. Maybe mine was older, but I believe it was the same model number.

[Sovereign85]

I recently experienced a same described problem with the Suburban NT-30SP furnace in our 85 Airstream Sovereign. The furnace is about 13 years young and suddenly died during our travels. We were fortunate to locate an independent RV service center with a competent technician who corrected the problem in about two hours. The work was preceded by testing the propane water column, regulator, and available electric current (which were okay). Then came replacement of the “circuit board” with a Dinosaur Fan 50 Plus Pin igniter control board, and replacement of the non-functioning limit switch. Parts and labor totaled $281.00, and the furnace now keeps us toasty warm.

Our NT-SP30 furnace is located on the floor under the range oven. It must be removed from inside the trailer, as there is no exterior access door.

It is doubtful you need a new furnace - a pricy venture. The water column test will verify propane pressure making gas available to your multiple appliances.

Working with propane equipment is not a recommended DIY project for the average RVer like me. Stay warm and safe travels!

[Jim Foster]

There is a device inside the unit called a sail switch that checks to see that the blower is blowing air. Sometimes that sail switch goes bad or gets hung up with debris and does not allow the gas valve to open.

A friend with an older brandX motor home had a technician remove his Suburban and take it to the shop. Found a bad circuit board. Repaired it, bench tested it, re-installed it, and it still would not light. Technician removed it again, put it in his truck and started to go back to the shop, but did not. Technician came back to the coach and found that there was no gas at the pipe. He looked under the coach and found that someone had disconnected the line and plugged it off, Probably because they did not want gas supplied to a furnace which was not working. Gas line hooked up and all was well.

You never know what was done before you got your unit.

[Grosspoluter]

Ditto on the sail switch
I removed the heater on my 345
I did a little research here on this GREAT forum and bought a dinosaur circuit board and sail switch it now works great
Yes I had to disconnect everything and pull it out through the inside cabinet then remove the sheet metal cover as I remember the sail switch was a little hard to find / see
The good news is while the unit is out you can clean every thing up oil the motor and if I recall right you can even remove the motor brushes and clean up the amateur etc.

[Streamracer]

I had the same problem and bought a new board and it worked one or two times and went back not lighting. First off make sure you have good voltage to the heater. Then what you hear clicking is the sail switch working when the blower gets up to speed. What mine was doing is the gas solenoids on the side of the heater were sticking and not opening when it called for gas. I disassembled it and cleaned. Now it works every time and I have a spare board.

[ijustlee]

A bird built a nest in the air intake of my furnace one summer. When I turned it on the first time in the fall it wouldn't light due to lack of airflow for the sail switch. Must have been a real small bird to fit through the slats on the Suburban intake grill. There is a small port on the firebox that can be opened to see if the electrode is sparking, when I looked in there I saw straw and twigs that had been sucked in from the nest and that clued me into that problem. A few other times I've got it to light off by cleanung the electrode with fine sandpaper. No spark can be a bad board or a stuck or defective sail switch. Assuming there is no bird nest of course!

[Air83]

If this is the original furnace you will want to replace it. A 33 year old furnace will get normal rust and develop pin holes which will leak carbon monoxide into your trailer. Also make sure you install a carbon monoxide detector. My 83 did not have one in the trailer. Most repair shops will not touch a furnace over 10 years old for this exact reason.

[LY007]

Good points, thank you all. As much as I prefer to fix rather than replace things, if this repair is going to run me much over $250, I think I might buy a new one as I have seen the new NT-30 model for as low as $440, plus the leak peace of mind, etc.; my only real concern is if the exterior vents line up.