Furnace doesn't light at altitude

[wabbles]

The Suburban furnace on a brand new Glacier Peak 5er won't light above 7,000 feet elevation. The furnace works fine up to about 6,000 feet. The trailer manufacturer says it is a "simple adjustment" but refuses to give the dealer "written" information. The furnace manufacturer states that their units are designed for use ONLY FOR USE BELOW 4,500 FEET. They say they put a sticker on the furnace and a note in the owners manual. Of course not one salesperson will ever tell a customer that. We have had two RV's in the past and the furnaces have always worked at altitudes up to 10,000 feet so maybe Suburban has "improved" their design to provide higher efficiency in the form of just don't use the furnace.
So now neither the RV manufacturer or the furnace manufacturer is offering to help. Does anyone have a suggestion or know of a furnace that is really designed to work?

[Padlin]

I've seen a number of problems reported with furnaces, fridges, hot water heaters when folks get up over 10k. Kind of a hit or miss thing, some units have the issues, some don't. I'd look into what Rvpapa suggests.

[brholt]

If you the fan comes on and then turns off without lighting one potential problem is the "sail" switch. This is a switch that allows the gas to flow if there is sufficient air flow. At high altitude and running on batteries you may not be getting enough air flow.

If this is the case you might have the switch adjusted.

[Rvpapa]

Try turning main regulator down to around 9". Done this many times in the Rockies at higher elevations. The water heater will probably work better too. Don't forget to re-adjust when you are lower down.
Art.

[JaxDad]

Before you get too excited blaming the furnace, check that your tank was not filled with a butane rich summer mixture of LPG which is the actual culprit.

With increased altitude and de erased temperature that might just be enough to change things enough that it won’t stay lit.

Get down and watch it cycle, I’ll bet you find it lights then immediately goes back out.

[enblethen]

Some furnaces have an air adjustment.

[SDcampowneroper]

Yes! At high altitude low atmospheric pressure results in a too rich combustion resulting in a ' flame out' . You will hear and see an attempt to light. Your regulator output pressure or orifice size needs to be reduced to match altitude. When it does light a soft quiet light with a lazy yellow flame shows a too rich mixture. Soot would be apparent.
We have had the obverse effect when going to sea level, the furnace would 'flame out' from too much air. When it did light, it roared like a jet engine, so-- I restricted the air intake a bit with my fingers until I found the sweet spot. then covered that much with tape.

[enblethen]

Model of Suburban furnace?