Heroku error

Also searched as: heroku crashed

Updated 11 October 2026

Short answer

Heroku's "Application error" page doesn't say what went wrong, but its logs do: every failure has a code. Run heroku logs --tail (or open logs in the dashboard) and look for code=. H10: the app crashed or didn't boot in time. H12: a request took longer than 30 seconds. H14: no web dynos are running, usually because they were scaled to zero. R14: the app is using more memory than its dyno allows.

What's the problem

Visitors see Heroku's "Application error" page, or your app returns 503 errors, often right after a deploy or when traffic picks up.

Why it happens

  • H10, app crashed: the app threw an error at startup or while running, often a missing config var or a missing dependency.
  • H12, request timeout: a slow database query or outside API call.
  • H14, no web dynos: web dynos scaled to 0, or no web process defined in the Procfile.
  • R14, memory quota exceeded: a memory leak or too many workers for the dyno size.

How to fix it

  1. Read the logs: heroku logs --tail, and find the code= on the failing requests.
  2. For H10, scroll up to the app's own error just before the crash. Check config vars and dependencies.
  3. For H12, find and speed up the slow request, or move the work to a background worker.
  4. For H14, scale up with heroku ps:scale web=1 and check your Procfile defines web.
  5. For R14, reduce memory use or move to a larger dyno.
  6. Roll back to the previous release if a deploy caused it.

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Sources

  1. Heroku: Heroku Error Codesofficial docsA crashed web dyno or a boot timeout on the web dyno will present this error.
  2. Heroku: Heroku Error Codesofficial docsAn HTTP request took longer than 30 seconds to complete.
  3. Heroku: Heroku Error Codesofficial docsThis is most likely the result of scaling your web dynos down to 0 dynos.
  4. Heroku: Heroku Error Codesofficial docsA dyno requires memory in excess of its quota .
  5. Heroku: Heroku Error Codesofficial docsTo fix it, scale your web dynos to 1 or more dynos: $ heroku ps:scale web=1
  6. Heroku: Loggingofficial docsYou can tail your logs using --tail (or -t ).

Related

Node crash By default, an uncaught exception makes Node.js print the stack trace and exit. Read that trace, fix the error, and run Node under a process manager. 504 Gateway Timeout Your app took too long to answer and the server in front of it gave up. Usually a slow database query, a slow outside API, or an overloaded server. Out of memory: process killed The server ran out of memory and Linux killed a process to survive, often your app or database. Confirm it in the system log, then find what used the memory. Backend down: server unreachable Check whether the backend answers at all: no response points to the server, DNS or firewall; an error code points to the app or its database.

Preventionlabs is independent and not affiliated with Heroku. Product names are used only to describe the problem.

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