ruby on rails 3 - 500 error page not showing on Heroku -

i'm trying custom 500 error page show on heroku, running rails 3.2.11

i've followed steps at: https://devcenter.heroku.com/articles/error-pages

the process worked fine maintenance page, doesn't seem work error page. i'm positive s3 url correct in heroku, , when visit s3 url directly can view error page fine (it set public).

config.consider_all_requests_local set false in production.rb

any ideas why heroku not showing it? blank screen in various browsers (chrome says it's 500 error doesn't render page).

the heroku's custom error page isn't displayed whenever exception occurs in application.

your application responsible displaying kind of pages.
see using exceptions_app rails 3.2.

the error page happens when error occurs heroku.

the devcenter page error pages says, testing error page :

to test error page, can push bad deploy such putting syntax error key configuration file, or creating path on app sleeps 35 seconds (thereby triggering error h12 request timeout.