I know nothing about what sort of coach you have, but I have read that a common problem with new E-series class c chassis and likely on A coaches too, is a twisted fuel line.
The chassis manufacturer provides a fuel hose for filling the tank, then when Thor builds the house around it, they install the hose attaching it to the side wall or wherever it goes.....
Apparently, they either
a) manhandle and twist the thing to force it to fit, or
b) modify the factory fill hose to extend or move it
with the end result being a twisted fill hose causing exactly the problem you describe.
Crawl under and have a look at the fill hose and connections.
Probably an easy fix.