Heating at Altitude

Remove the round foil duct between the heater case and the grille.  Just put the grille back on without the duct.

 

Removes a restriction allowing more air to flow.  Low air flow can prevent the sail switch from activating.

 

Restricted air flow can possibly cause motor overheating then, tripping the thermal breaker inside the furnace.

 

Removed it on mine.  No more problems since I did that to mine at elevations up to 10K feet.

Thank you so much!  when I get back from Canada I am going to try this first thing.  Great advice Sir!  I will you updated to my progress for sure. 

for those that are here with the same problem , I found this video helps a lot : 

 

 

 

Late to this...but last Fall in Winds I spent 4 nights at 9,400+ with temps in mid 20's...heater/stove worked perfectly...2016 Hawk...

Yes remove the duct work. 95% certain that is your issue.

We have the Propex furnace with only moderate insulation. Have used it with no problem in below zero temps and altitudes over 10K. Maybe we are lucky, but installing the same on a new camper so hope to have similar results

Aside from issues with propane, thermostat, or the furnace control board, many furnace problems revolve around the sail switch. the furnace requires sufficient air flow from the blower to activate the sail switch for safety purposes. Anything that impedes that can result in the furnace not being able to start: failed or dirty sail switch, low battery, high altitude, back pressure from the ducting (anything resulting in lower flow rate), etc. These impacts are cumulative. Adressing one or more of these issues usually resolves the problem. Many have found that removing the ducting is a good fix that increases the air flow enough for the furnace to work at high altitude.

FWIW, our furnace worked fine at high altitude for the first ~1.5 years, but on our last trip above 8000' it started to click on and off. I suspect I will need to clean the sail switch or remove the ducting before our next higher elevation trip.

Remove the round foil duct between the heater case and the grille.  Just put the grille back on without the duct.
 
Removes a restriction allowing more air to flow.  Low air flow can prevent the sail switch from activating.
 
Restricted air flow can possibly cause motor overheating then, tripping the thermal breaker inside the furnace.
 
Removed it on mine.  No more problems since I did that to mine at elevations up to 10K feet.

It’s this. Same thing here.
I didn’t like removing the foil ducting completely. In my case, I was able to modify the exit vent (now just a grate) to reduce restriction and furnace now lights at higher altitudes.
The tortured path of the venting to the output is just obviously bad design.p, and I sincerely hope FWC fixes this for future owners.

+1 for air flow being restricted. I camp every weekend at 8500 feet have had nothing but issues. All issues pointed me towards a bad sail switch. After replacing 2 sail switches I deduced that was not the issue. 

 

The furnace works fine at home at 4000 feet, but up in the mountains it just wont stay lit. This weekend while cursing the furnace and freezing my A$$ off I decided to remove the center plastic piece that allows you to direct airflow on the front of the furnace inside the camper. BOOM she fired right up and stayed functional with 0 issues. I tried replacing the plastic cover and the furnace clicked right off. Pull the plastic piece off and she lit right back up.

 

I think at high MSL altitudes just removing the ducting wasn't enough. Try removing the plastic cover in front of the furnace output and see if that works. 

+however many we're at now.. remove the ducting. I bet it fixes your issues.

Fwiw, my factory furnace in my 2016 Grandby worked perfectly at 16000 ft. The last good one installed I think. 🤷‍♂️

16,000’? Where was that KP?