Unpublish content problem on update
If you're using the Rules module, here's a simple rules export for the purpose.


Event: node_presave 
Condition: authenticated user 
Action: unpublish node


You could change the role condition to suit your site user config.

e.g: Add the role condition "Adminstrator" and click the "Negate" checkbox for "NOT Administrator role" condition.

You could also, for example, add a Rules action to show a message under "System > Show a message on the site" after unpublishing the node.



Exported Rule:

{ "rules_unpublish_updated_content" : {
    "LABEL" : "Unpublish updated content",
    "PLUGIN" : "reaction rule",
    "REQUIRES" : [ "rules" ],
    "ON" : [ "node_presave" ],
    "IF" : [
      { "user_has_role" : {
          "account" : [ "site:current-user" ],
          "roles" : { "value" : { "2" : "2" } },
          "operation" : "OR"
        }
      }
    ],
    "DO" : [ { "node_unpublish" : { "node" : [ "node" ] } } ]
  }
}


You can import the Rule at: 

/admin/config/workflow/rules/reaction/import