TinyMCE is missing the H1 tag

I’ve installed modx into a number of sites, but the last few installs the H1 tag is missing from the drop down list. Any ideas on how to fix this?

To get it back see http://modxcms.com/forums/index.php/topic,48639.msg284678.html#msg284678
or http://modxcms.com/forums/index.php/topic,47506.msg280295.html#msg280295

More issues http://modxcms.com/forums/index.php/topic,47886.msg280918.html#msg280918

Thanks