Furnace runs but will not ignite

When it did run, what did the flame sound like? Do you hear the flame attempt to light? If so, its not the sail switch or gas valve or supply.
Mine used to lock out regularly like yours, until I realized when it tried to light or did eventually the flame was noisy, rough & loud. Turned out the fan was blowing the flame off the burner, so I slowly restricted the air intake with tape until it quieted down. Works perfectly now.

Maybe a bad thermocouple??

If you have propane and it is turned on....then
Sounds like a stuck or faulty "sail switch."



When the air flow from the blower does not trip this switch, the furnace will not ignite. It's one of the many safety backups on an RV furnace.

Are the tanks full? The regulator may have frozen up during last nights cold temps, even just partially, reducing propane flow to the ignitor. The propane valve in the furnace may not be opening, either frozen, stuck or failed. The fact that you hear the ignitor indicates there is no problem with air flow, thermostat or the majority of the furnace control board.