furnace won't light at elevation and cold

[IDPaddler]

Hello,
I got a brand new 2022 hawk the spring. I took it out a handful of times in cooler weather and the furnace works fantastic. Coldest nights/mornings probably upper 30s. Elevation not more than 5000 feet. Haven't used the furnace all summer.

Did a trip this weekend to the mountains. Was probably between 6500–8700 feet. Tried to light the furnace late in the evening, probably high 30's- low 40's. The fan would come on each time without issue. I would hear the clicking of the igniter followed by the whoosh of it lighting up (I guess that's what that sound is). However, the whoosh sound would only last for a few seconds before "burning out". After multiple tries the whoosh wouldn't even happen.

We bundled up for a chilly night. It was in the low 30s the next morning. Not surprisingly, the furnace wouldn't light. Interestingly, the stove would barely light. I could hear and smell (though not that strong) propane but it was a very weak flame. After a while and multiple tries the stove returned to normal function.

We drove up to about 8700 feet and went hiking all day. Temperatures were in the mid 50s. Back at the camper in the early evening I decided to try the furnace again. Much to my surprise it lit and stayed lit! I turned it off to see if it would work again. Unfortunately, it was one and done...never lit again.

Today at home at 2700 feet it's in the 60s and everything is working flawlessly.

I know this wasn't a power issue because my batteries are brand new and my solar panel was reading fully charged/float mode.

Any ideas what was causing the issue? I've done a little reading and it sounds like elevation and cold temps can cause problems with the pressure regulator? I never had this issue in a pop-up trailer I used to have. I've had camp stoves burn a little weak at elevation/very cold temps but they always worked.

Any ideas?

Thanks

 

[Wandering Sagebrush]

There are several threads on this in the FWC sub forum. IIRC, it’s because of ducting that is causing back pressure that keeps the sail switch from allowing the furnace to lighting. I believe the solution was removing the ducting. Stan Kennedy had weighed in on it, too.

Check the forum. If you can’t find it, send me a PM, and I’ll try and find it for you.

edit: https://www.wanderthewest.com/forum/topic/23692-atwood-furnace-sail-switch/

https://youtu.be/iJq7As3brCM


one of the last posts in this thread.

 

[ski3pin]

Since you say the stove had a weak flame also, it could be that you turned on the gas at the tank too quickly overpowering the overflow protection devise. Turn off the gas at the tank, discontent the supply hose, reconnect the supply hose, and then turn the valve slowly to turn the gas supply back on.

 

[IDPaddler]

Great. Thanks for the replies and the links. I've had a look a the vid and done some more googling. So is the thought that with colder air the sail switch is not functioning as it should?

 

[Wandering Sagebrush]

Great. Thanks for the replies and the links. I've had a look a the vid and done some more googling. So is the thought that with colder air the sail switch is not functioning as it should?

I don’t believe it’s temp related, but rather density. If your camper has the issue with the ducting restricting out flow, that might be contributing or the root cause. Some members have removed the duct, and simply let the warm air flow through the louvered vent.

 

[IDPaddler]

I don’t believe it’s temp related, but rather density. If your camper has the issue with the ducting restricting out flow, that might be contributing or the root cause. Some members have removed the duct, and simply let the warm air flow through the louvered vent.

I guess I'll remove the duct if/when it happens again. Thanks for taking the time to reply.

 

[Old Crow]

Since you say the stove had a weak flame also, it could be that you turned on the gas at the tank too quickly overpowering the overflow protection devise. Turn off the gas at the tank, discontent the supply hose, reconnect the supply hose, and then turn the valve slowly to turn the gas supply back on.

Stan tells us about this problem in the following video.... (I have the video starting at the 1:30 mark)

Propane Tanks use review

 

[UmkaAndHawk]

As already state in the thread, a likely explanation is back pressure from the poor ducting design which limits the air over the sail switch, and is a problem when the air is too thin (at altitude). We had exactly this problem with ours.

We did *not* wind up having to remove the ducting completely! Instead we were able to remove just the louvers in front (and replace them with some metal screen to keep out fingers) and this was enough.

I don't love the idea of removing the ducting completely if you don't have to because then the furnace will end up eating even more of its own air, which obviously works but I felt was sub-optimal.

Good luck!

 

[IDPaddler]

As already state in the thread, a likely explanation is back pressure from the poor ducting design which limits the air over the sail switch, and is a problem when the air is too thin (at altitude). We had exactly this problem with ours.

We did *not* wind up having to remove the ducting completely! Instead we were able to remove just the louvers in front (and replace them with some metal screen to keep out fingers) and this was enough.

I don't love the idea of removing the ducting completely if you don't have to because then the furnace will end up eating even more of its own air, which obviously works but I felt was sub-optimal.
Good luck!

Thanks for the reply! I'm pretty certain this was the issue. I'm glad to know there is a work around. It would be totally ridiculous if these furnaces were obsolete at low temps and/or elevation.

 

[MountainSufi]

FWIW, both my dealer & I have found the Honeywell digital thermostats are unreliable. I've happily replaced with the "old fashioned" analog model. Buy a spare; it's cheap & takes littler room in your store space.

 

[Wallowa]

Thanks for the reply! I'm pretty certain this was the issue. I'm glad to know there is a work around. It would be totally ridiculous if these furnaces were obsolete at low temps and/or elevation.

Counter point...the furnace in my 2016 Hawk, unmodified, has worked perfectly at -15 F and at 9,800 ABSL....of course we are only a sample of 1.

 

[Mthomas]

Counter point...the furnace in my 2016 Hawk, unmodified, has worked perfectly at -15 F and at 9,800 ABSL....of course we are only a sample of 1.

Scame here, 2018 hawk up to 10,300 ft but not so cold and I replaced the analog thermostat with a digital. Key is lithium batteries which will continue to operate properly at low temps. N=2

I think that the design of the low amperage model heater, which is already operating at a minimal airflow to keep amp usage low, does not allow for even a tiny restriction of the airflow. I think some of the campers are assembled with just enough of an offset from the heater to the register that there is a bit more air restriction in the duct and …no heat at lowered air density, or low voltage in batteries. Either way, not enough flow and sail switch cuts it off.

 

[AWG_Pics]

Counter point...the furnace in my 2016 Hawk, unmodified, has worked perfectly at -15 F and at 9,800 ABSL....of course we are only a sample of 1.

Knock on wood, but we have had no issues with our 2019 Hawk furnace. Have camped at over 8,000 feet several times at over 9,000 at least once.

 

[Weissenheimer]

I have to say I believe it is more an issue of a dirty sail switch and less about the resistance from the 3" of ducting and slight bend (lmfao). Mthomas may be right about these heaters running at the "bare minimum" to activate the sail switch, but how come my heater kept working even at 11.7 volts (batteries were toast) with the ducting installed? I have still had my heat fail at 12.8v with new batteries too. Every time it does fail (twice a season maybe). I take apart the switch and find "belly button lint" in there. It appears to be just enough to prevent the microswitch from activating. I don't have any pets, this lint is just what you get with a recirculating system in a small space. Although a better switch design could prevent this and I believe there is one out there P/N 33081 or something. Sometimes I have to fully take apart the sail switch but I have it down to 5 minutes and the heat always comes back without fail. Mind you I am at sea level so maybe this is a case of stacking deficiencies and not always one single thing

 

[IDPaddler]

I have to say I believe it is more an issue of a dirty sail switch and less about the resistance from the 3" of ducting and slight bend (lmfao). Mthomas may be right about these heaters running at the "bare minimum" to activate the sail switch, but how come my heater kept working even at 11.7 volts (batteries were toast) with the ducting installed? I have still had my heat fail at 12.8v with new batteries too. Every time it does fail (twice a season maybe). I take apart the switch and find "belly button lint" in there. It appears to be just enough to prevent the microswitch from activating. I don't have any pets, this lint is just what you get with a recirculating system in a small space. Although a better switch design could prevent this and I believe there is one out there P/N 33081 or something. Sometimes I have to fully take apart the sail switch but I have it down to 5 minutes and the heat always comes back without fail. Mind you I am at sea level so maybe this is a case of stacking deficiencies and not always one single thing

I'm inclined to think if it was lint in the sail switch it wouldn't come back on until cleaned. My heater failed at elevation (7-9.5K ft) and low 30 degree temps. It fired right back up when I dropped back down to 2800 and warm temps. Hasn't failed since.

I'm going out this weekend. Weather is gonna turn wintery in the high country. Might just make a side trip up to ~7600 for the night and see what happens. Bringing a Mr. Buddy just cause I can!

 

[Wallowa]

Concur...from what I have read the "improved' sail switch is the same as the old one but with a different base mount [82 vs 81]....hence, it seems logical to assume that debris [belly button lint ] inhibits the sail switch movement thus it does not make electrical connection and start ignition of furnace. Lower elevations have higher air density and perhaps that increase air mass will move a slightly compromised [clogged] sail switch....

Has anyone actually taken out a sail switch that "failed" to start a furnace and confirmed that the circuit [electrical contact] was defective therefore stopping the electrical furnace starting signal?

 

[pvstoy]

Interesting thought that somebody can try... Has anyone hot wired the switch to tell the heater computer that the air flow is working and light the burner? Like the thermostat you can bridge the wires to get the heater to run, then un-bridge the wires to stop the heater. Timing for bridging the sail switch wires may be more critical and disconnecting them.

I guess that would be a way to get heat if it is the sail switch that failed to see if it would work by you being the switch. Hey if that did not fix it then you might have other problems associated with the heater.

 

[Jsoboti]

I had the same issue, removing the ducting only worked somewhat. The ultimate fix for me was to simply remove the plastic disk on the very front of the furnace that swivels and diverts air to the sides.

Simple to do and my furnace works 4.0 at 8,500 feet where I usually camp in the winter. Hope this helps!

 

[IDPaddler]

I had the same issue, removing the ducting only worked somewhat. The ultimate fix for me was to simply remove the plastic disk on the very front of the furnace that swivels and diverts air to the sides.

Simple to do and my furnace works 4.0 at 8,500 feet where I usually camp in the winter. Hope this helps!THanks

Thanks for the post. I'll try that first if/when it fails again.

Well I was out for 3 nights with last night down the mid 30's and snow line less than 1000ft up. Furnace worked like a champ, albeit only 1800 ft or so.

Untitled by cory shuler, on Flickr

 

[Weissenheimer]

Interesting thought that somebody can try... Has anyone hot wired the switch to tell the heater computer that the air flow is working and light the burner? Like the thermostat you can bridge the wires to get the heater to run, then un-bridge the wires to stop the heater. Timing for bridging the sail switch wires may be more critical and disconnecting them.

I guess that would be a way to get heat if it is the sail switch that failed to see if it would work by you being the switch. Hey if that did not fix it then you might have other problems associated with the heater.

I do believe someone mentioned this before in another forum and they said the furnace is smart enough to not allow this type of hack. The furnace will refuse to light if that switch is already closed before the blower starts spinning, it knows something is up. But it makes me wonder if a hard wire switch could be manually activated a couple seconds after the blower kicks on, and that would successfully trick it? However you'd have to manually attend your furnace every time it wants to kick back on lol.