Why it will not start sometimes
Could be any number of reasons. Could you give us some more information? Number of miles on your Routan, transmission, when it won’t start is the weather always the same (raining vs not raining), when it won’t start is that the first time that day you tried to start it or subsequent time(s)?
Does it turn over? If not, the copper solenoid contacts on the starter are possible. But first: is the battery charged and are its connections secure?
Is the battery original? Are the connections clean?