Bad link to favicon in header but can't find where to edit

Using Organico theme. Site is http://www.guttergardens.com

I had a working favicon.png file but it stopped working. Thought the file had been damaged or deleted but it is still there. Have had some others working on the site. If I look at source when viewing the site (not as admin) I can see the bad link in the head section – there are a few added characters in the path.
I have looked at header.php files in the theme and a number of other files. Tried appearance in the admin panel too. Where can I find the link to edit?