I recently redid my RSS feed and have noticed that RSS ver 2.0 seems to prefer an entity number rather than an entity name.
For example if I use %temp% which includes the degree sign the feed does not work and the Validator returns an error “undefined named entity” and points to " °F " as the problem.
However if I use %tempnodp% and insert the entity number for the degree sign followed by “F” (in my case but it might be C for others) in the code all is well.
Hopefully this observation will be of use to someone.