Peternliane,
Safety first. If you have a continuing smell of propane, this is abnormal and DANGEROUS and unless you're sure you know what you're doing, you need to shut off the furnace and the propane supply and get a certified tech to help you.
If the furnace blower is running, but no heat coming out, and the propane smell is only when you try to start the furnace, you may have a safety lockout condition where the furnace tries to light and fails. In this case, there may be a temporary smell of the gas from when the furnace tried to light.
When the thermostat calls for heat, the furnace blower comes on. If the blower gets up to speed, it activates a Sail Switch that allows the circuit board to turn on the gas valve and operate the direct spark ignition. If the propane ignites, you may hear a whooshing sound from the burner. A flame sensor confirms that the burner has successfully lit and allows the propane valve to stay open. If the flame sensor doesn't confirm the burner has lit, it closes the gas valve as a safety measure. The blower may continue to run and the furnace may go into a lockout condition. You have to turn off the thermostat (change mode) to reset it.
The most common cause of failure is poor propane flow. You may have enough flow to light the burners on the oven, but not enough to run the furnace. If it's almost enough, the burner may ignite but produce only lukewarm air.
Take a look at your propane supply. You may have a failing pigtail or failing regulator. Try changing over to the other tank manually. Try swapping the tanks. If either of these resolves the problem, you've confirmed the problem.
Also look at the furnace vents. One is intake and the other is exhaust. If blocked, or if something has gotten into the vents, it could be interfering with combustion.
Also make sure you haven't blocked the furnace air return inside the RV. If you covered it or put something in front of it, it might be reducing air flow and preventing the blower from running at full speed.
If you've blocked heat registers to try to redirect heat, you can also cause problems, possibly including failure of the over temperature safety sensor.
Again, if you have continuous smell of propane, that's abnormal and very dangerous. Get help.
Here's a link to our Heating and Cooling Guide, which includes some of this information. The furnace info starts on page 15.
Please let us know what you find.
