The older propane appliances would have a small flame on a tube that was the pilot to light the burner when the thermostat opened the valve for the main burner. A small thermocouple (copper heat sensor rod) would shut off the gas flow to the pilot if that small pilot flame went out.
Modern would have an electric ignition with some gizmos to open gas valve to burner AND start component sparking or glowing to ignite the burner in response to thermostat. Furnace will shut off gas if it doesn't detect burner ignition. Burner has the same sort of copper probe thermocouple that when heated generates small amount of current.
So there would always be a small flame burning in an old style furnace until know is turned to pilot. In pilot position one can push in the knob to open the pilot gas flow and light it. Holding it for a minute or two until the sensor gets hot. I think on some models in the pilot position if the knob isn't being pushed in the gas flow to the pilot gets cut. Same as off. It sounded like OP and gas guy were describing that. Knob at pilot and the little flame goes out.
The burner is essentially a fire in a box that has a vent to pull in outside air for combustion and an exhaust vent to take the combustion gases outside. Won't use up the air inside to support the combustion and won't dump the CO from combustion inside.
The room air gets warm by flowing around the box with it's vents to the outside. Like a wood stove if the wood stove had a pipe in the back that brought in air for combustion and the door sealed air tight.
If that box has rust holes or cracks at the welded seams the leaking CO can kill you so hat is why checking the box for CO leaks
is important professional service item. When it looks like the stars in the sky when lit in the dark you have a lot of holes. Also why finding a spot for a CO detector in your camper is important.
Having a 77 Scamp
I have given some thought to the furnace age. Thought about 2 things.
Doing bodily harm to the engineer who put the dang hot box right next to the bed where sheets and blankets can fall
against it. The outer metal shouldn't get hot enough to ignite cloth but I am sure I don't want it melting my expensive sleeping bag either.
That there are pro and cons to the old vs new furnaces. Convection furnace has no blower, thus draws no power from battery
. It might use a bit more gas because it cycles slower but I have days worth of propane, not days worth of battery
sensor. Modern furnace has that thermocouple positioned where if the oxygen
level is low it causes the pilot flame to be smaller and it won't keep the thermocouple hot so furnace shuts down. Supposed to be a safety feature, if the fire box leaks
and starts contaminating the atmosphere with CO and using the oxygen
the furnace quits.
On the other hand above 7,000 feet there isn't as much oxygen as it takes to make the flame reach the thermocouple and the furnace cuts out. Not being able to keep furnace lit on a chilly night in the mountains sort of stinks.
My furnace works, smells like burning dust since the vent pipes are covered in dust and I never use it but I do test it annually. I would be inclined in a small camper like mine to get a little cube heater for when I have electric available and a small propane heater that I can set on the counter that aims outward. You can take the chill off in the morning by making a pot of coffee and gain 10* or more over outside temperature from a burning candle.
Would take very little btu's from a portable heater to make things fine for sleeping. Cody Wyoming snow on the car in the morning and a small electric cube heater had no problem keeping it warm all night.
If you are going to use a candle make sure it is in a sturdy, stable, fire proof container. I would consider setting a long burning candle in a metal coffee can in the sink safe. But I'm a bit of a... well not sure what but have done that. Have also slept burrowed into a mound of snow with a candle lantern hanging from a branch shoved into the wall of the snow cave so... I have standards but not ones everyone will share.
For portable propane heater consider models with some care and test, make sure that if you place it on counter it doesn't overheat anything like counter or rising heat getting the overhead cupboards. I'm not going to suggest a brand or model because frankly that is a pretty contentious issue. Some folks use outdoor heaters inside, others are aghast at such behavior they consider dangerous. I can only say it would have to be fairly cold to need more than 5,000 btu's
A propane lantern on low can keep a 4 man tent warm in Michigan winters. Getting up to use the bathroom means leaving the sleeping bag and that is not pleasant but it does stay above freezing through the night.