RV Repair: 8531-11, furnace blower, gas valve

Question
my furnace blower kicks on but it does not light,it lit once
a few days ago but has not lit again since.
what could be the cause of this

Answer
plugged regulator   out of propane   are the most common causes.  then you get into actual bad parts.  The gas valve, the safety shut off, or ingniter.

good luck.  sorry so long with response.  I was camping the last two weeks and forgot to turn off the all experts questions.