Try this trick.
Make a super administrator, I call him "noeditorguy". and then find him in the user manager and change his editor to "No Editor".
Any time I need to work in raw html, I log in with this user, front end or back end.
This also works for articles too.
Note,
if you are showing authors on the front end article, you’ll either have
to create the article with the user you want to be author first, or
override the author in the parameters of that article.
Even Easier
Get an advanced editor like WsywiygPro, it allows you to flip to the source code and back and does not cause code errors.