Heater / Furnace Issues above 10k Feet...

[So Cal Adventurer]

Hey All

2018 Hawk

Just did a trip to the sierras. Had some issues above 10k.

Heater/Furnace worked fine at 7-8k feet.

Above 10k the fan would turn on, but no clicking or attempts to light, and then the fan would shut off, many attempts to try this over 2 nights above 10k.

Removed large outside panel, it would click and fire up, but die within a minute.

If i put the panel back on, it would die immediately. Almost like it was starving for air.

Got back down to 7k feet, everything worked fine again

Full propane, batteries fully charged.

For poops and giggles, i tried the hot water heater several times above 10k and it worked flawlessly and fired up instantly every time.

Any ideas? I was stumped... and cold! hahaha

Thanks
kevin

 

[MarkBC]

Just a a guess -- an "idea": Because the air density was low at 10,000 feet there wasn't enough force to swing the sail switch far enough to switch on the lighter. I'm suggesting that because you said you didn't hear the "click" under those conditions.
Another situation -- similar but different -- where the furnace won't start is when the fan isn't turning fast enough (due to low battery) to swing the sail switch -- - I've experienced that. So maybe low air density could have the same effect...maybe.

 

[So Cal Adventurer]

Thanks Mark

Yeah, from all the troubleshooting tips i've read, that seems to be the issue.

My dilemma is, how do i fix it?

 

[Optimistic Paranoid]

Have you tried contacting the furnace manufacturer? Maybe there's an optional part, or a known work-around.

Btw, with catalytic heaters, there's a low oxygen cut-off that causes exactly the same problem at high altitudes. But I've never heard of a furnace that had one.

 

[CougarCouple]

Hi So cal adventurer

Look at the end of the burner, there should be a shutter look to see the position. Might bee adjustment.
Just a thought.
Russ

 

[PokyBro]

Hi So Cal Adventurer,

The way you have described the furnace functioning, I’m wondering if it is all related to pressure. Clearly your pressure regulator is working below 7,000 feet, but perhaps with a full tank at 10,000 feet it seems to be malfunctioning. There is sequence of events that occurs when these furnaces start up. First the fan engages the sail switch, then after 30 seconds or so it should click and ignite. It something is off on the pressure exerted by the gas, it will cause a fault and shut everything down. Same thing happens if the sail switch is faulty, the fan shuts off. Some furnaces have a grid by the control board. On mine there is an led light that flashes and pauses. The grid tells you the fault by the sequence of flashes and pauses. Anyhow I’m just guessing about the fuel pressure difference with a full tank at 10,000 feet vs 7,000 feet. You might try shutting off the propane tank, unhook the hose, hook back up, and open valve very slowly. Worth a try. Must have been frustrating not having heat when you needed it.

Poky

 

[So Cal Adventurer]

Hi So cal adventurer

Look at the end of the burner, there should be a shutter look to see the position. Might bee adjustment.
Just a thought.
Russ

Thats what i was thinking... Its a sealed unit as far as i can see.. hmmm

 

[So Cal Adventurer]

Hi So Cal Adventurer,

The way you have described the furnace functioning, I’m wondering if it is all related to pressure. Clearly your pressure regulator is working below 7,000 feet, but perhaps with a full tank at 10,000 feet it seems to be malfunctioning. There is sequence of events that occurs when these furnaces start up. First the fan engages the sail switch, then after 30 seconds or so it should click and ignite. It something is off on the pressure exerted by the gas, it will cause a fault and shut everything down. Same thing happens if the sail switch is faulty, the fan shuts off. Some furnaces have a grid by the control board. On mine there is an led light that flashes and pauses. The grid tells you the fault by the sequence of flashes and pauses. Anyhow I’m just guessing about the fuel pressure difference with a full tank at 10,000 feet vs 7,000 feet. You might try shutting off the propane tank, unhook the hose, hook back up, and open valve very slowly. Worth a try. Must have been frustrating not having heat when you needed it.

Poky

Thank you! Excellent idea! I will check this out.. Not sure when ill be above 10k again, but i would like to be ready

 

[ardvark]

Rather than try to puzzle it through, just call the furnace manufacturer. Both Atwood and Suburban both have customer support. Suburban in particular is excellent. I have not called Atwood since the Dometic buyout.

The regulator is all or none in terms of opening it manually. Pressure can be set or changed, but you do need a manometer to track the change. I would have the pressure checked before doing anything else. The furnace should operate within a pressure window of about an 11-13" water column.

 

[RajaZoie]

If the furnace has a built in carbon monoxide shut-off that can also trip above 10,000' due to the lower oxygen content. Before our truck camper we were warned about that with our portable propane heater that had a built-in CO shut-off.
We've regularly camped around 9k' without issue but have not gone above that with our Hawk.

 

[ardvark]

Furnaces to not have built-in CO cut-offs like portables do. Since an RV furnace burns only outside air, they do not pose a CO risk unless taken apart and reassembled incorrectly. Cooktops and ranges are the only built-in RV appliances that utilize air within the camper. All others (fridge, water heater, and furnace) are designed to seal the burner to the outside.

 

[CougarCouple]

SCA
It is kinda strange that the heater won't work at all. In all honesty I knew you said furnace but when you said took the outside panel off, my mind went to water heater. Ours is pretty much sealed up and would have to disassemble to get to heater components. Would not recommend adjusting the regulator, maybe check the setting with a manometer. I think they are designed to work properly at any altitude, but that would be a question for someone else.

Found this

https://www.justanswer.com/sip/atwood?r=ppc%7Cga%7C2%7CCars%20-%20RV%20-%20Search%7CAtwood&JPKW=atwood%20furnace%20repair&JPDC=S&JPST=&JPAD=237627895630&JPMT=b&JPNW=g&JPAF=txt&JPCD=20171205&JPRC=1&JPOP=AES_Cars_ETA%203&mkwid=sZBK4K8yo_dt&pcrid=237627895630&pkw=atwood%20furnace%20repair&pmt=b&plc=&cmpid=12989842&agid=1461357688&fiid=&tgtid=kwd-4204152514&ntw=g&dvc=t&gclid=EAIaIQobChMIxICNwab12wIVFI9-Ch0AMwzuEAMYASAAEgKnifD_BwE


Russ