2.13.2.1. Problems while working with Joomla!
Error 503
If your site gets a 503 error, it might be due to a plugin.
You can try to temporarily rename the directory plugins... If the error goes away, the reason is in the plugins. In this case, you should turn off the plugins one by one, checking for an error on the site in order to determine which of them interferes with the normal operation of the site.