suburban nt-24 will not light at altitude

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ericbwy

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Joined
Oct 9, 2017
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ok here is the deal.
I have a suburban nt-24 that will not light when I am at 8000+ ft....the confusing part is it used to. :-\
what originally happened was that it was running perfectly and the wall thermostat decided to die on me. It was my last trip of the season so I took the camper down to my house at 3500ft. replaced the thermostat and it fired right up. The following season I took the camper back up to the mountains ( around 8200ft) and it goes through all the motions. Fan kicks on, sail switch activates, igniter sparks, you can smell propane but no ignition.
since all of this I have replaced the following
1. sail switch
2. limit switch
3. control board
4. igniter
5. regulator on the camper
6. cleaned all the intake and exhaust tubes.

Everytime I Bring it home (3500 ft) it fires right up on 12v without shore power. also has new batteries and full propane tanks.
I am at a loss and can not think of anything else to replace or clean. seems to me its a mixture issue but again intake and exhaust are clean and regulator is new and bottles are full. hopefully someone out there has an idea for me.
Thanks in advance.
 
Many of those types of WH have adjustable air intakes on the burner tube. At altitude since the air is much thinner it takes more air to get the same combustion. Have you tried adjusting the air intake while you are at elevation?
 
As you have learned, all those replacement things were a waste of money. Propane burners designed for sea level don't work reliably in the thin air above 5500 ft - your owner manual should say so. Somewhere around 8000 is gets really chancy. Why did it work before? Who knows?  The burner is very susceptible to the slightest variation of the air & gas flow/mix at the burner tube.

I've read that reducing the LP gas pressure helps the mix at high altitude. Being discussed in this topic on fridges at high altitude,
http://www.rvforum.net/SMF_forum/index.php/topic,105735.msg984920.html#msg984920
 
what do you mean by WH? water heater? this is a furnace. but all the same there is not an airflow adjustment. I have tried running it with the front cover off and it makes no difference. is it possible that the gas valve is weak? im just confused because of it working before the thermostat issue but not after.
 
Gary,
thanks for your response. I am completely confused on why it worked before and not now with originally only changing the broken thermostat. I have tried adjusting the regulator with no luck.
 
Obviously the thermostat had no effect. All it does is send a +12v "heat needed' signal to the furnace. Everything in the furnace works exactly the same, whether there is a thermostat or not. You could put a 12v battery on the +12v signal line and the furnace will try to run.  Something else changed, whether you are aware of it or not.

When you get to 8000+ ft, the conditions are definitely not favorable for ignition. It might work one day and not another. It might work at one campsite, but not another a mile down the road.
 
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