ErrorBase
Independent technical referenceOfficial site
  • Software and systems
  • HTTP service

502

HTTP 502 Bad Gateway: a gateway received an invalid upstream response

Verified with sources1 sourceReviewed Aug 22, 2026
Technician coming? See what they must show you

Risk level

Low

Usually safe to check without specialist tools.

Urgency

Medium

Quick answer

HTTP 502 means a server acting as a gateway or proxy received an invalid response from an upstream server while trying to fulfill the request.

Safety first

Stop and check this first

  • Do not disable TLS verification expose a private upstream or bypass the gateway as a generic 502 fix. Locate the invalid response boundary first.

Safe checks you can perform

  • Identify the gateway that generated 502
  • Check a safe upstream health path
  • Retry only after confirming the operation is safe

Leave these tasks to a qualified professional

  • Do not attempt this professional task: Trace the gateway-to-upstream response boundary

What a technician must be able to justify

A technician is coming

These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.

These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.

  1. Trace the gateway-to-upstream response boundary

    What they doThe platform operator should correlate the request across gateway and upstream telemetry then inspect connection protocol response framing and application health at the first invalid boundary.

Before accepting a part or repair

Nothing has been shown yet. Do not accept a part swap based on the code alone.

Checks and evidence, step by step

Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.

  1. 1

    Identify the gateway that generated 502

    Tools required

    Procedure

    Record response headers request identifiers endpoint and UTC timestamp so the operator can distinguish CDN load balancer reverse proxy and application gateway layers.

    Redact authorization cookies URL secrets and response details before sharing them.

    Evidence: RFC 9110 section 15.6.3 - 502 Bad Gateway

  2. 2

    Check a safe upstream health path

    Tools required

    Procedure

    If you operate the service use its documented health endpoint or one lightweight read request to determine whether the upstream responds normally outside the failing route.

    Do not bypass access controls or expose a private upstream directly to the Internet.

    Evidence: RFC 9110 section 15.6.3 - 502 Bad Gateway

  3. 3

    Retry only after confirming the operation is safe

    No special tools

    Procedure

    For a read request retry once after a short delay. For a write first verify whether the upstream accepted the original operation and whether an idempotency key was used.

    A gateway failure does not prove that an upstream write had no effect.

    Evidence: RFC 9110 section 15.6.3 - 502 Bad Gateway

Where this code applies

A code is meaningful only inside the right product and version context.

Primary scope

System
Software and systems
Brand
HTTP
Product type
HTTP service

Known code variants

  • 502 Bad Gateway
  • 502 Fehlerhaftes Gateway
  • 502 Gateway non valido
  • 502 Puerta de enlace incorrecta
  • Bosch 502 bici elettrica
  • Bosch 502 bicicleta eléctrica
  • Bosch 502 E-Bike
  • Bosch 502 eBike
  • Bosch 502 vélo électrique
  • Bosch eBike code 502
  • Bosch eBike error 502
  • Bosch eBike Fehler 502
  • Bosch eBike Fehlercode 502
  • code Bosch eBike 502
  • code erreur 502
  • codice Bosch eBike 502
  • código Bosch eBike 502
  • erreur Bosch eBike 502
  • error Bosch eBike 502
  • errore Bosch eBike 502
  • événement Fronius 502
  • evento Fronius 502
  • Fronius Ereignis 502
  • Fronius event 502
  • Fronius inverter 502
  • Fronius Symo / Eco 502
  • Fronius Wechselrichter 502
  • HTTP 502
  • HTTP status 502
  • inversor Fronius 502
  • inverter Fronius 502
  • onduleur Fronius 502
  • status code 502

What it means

The gateway reports the failure but the status alone does not identify whether the upstream application connection protocol or intermediary caused the invalid response.

Warnings and stop conditions

  • Higheditorial warning

    Do not disable TLS verification expose a private upstream or bypass the gateway as a generic 502 fix. Locate the invalid response boundary first.

    Evidence: RFC 9110 section 15.6.3 - 502 Bad Gateway

Symptoms and causes

Probable causes · in order

  • A gateway or proxy received an invalid upstream responseConfirmed

    RFC 9110 defines 502 as an invalid response received by a gateway or proxy from an upstream server while fulfilling the request.

    Evidence: RFC 9110 section 15.6.3 - 502 Bad Gateway

Virtual technician

Does 502 still appear after these checks?

Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.

Start diagnosis

Sources and technical references

  1. 1

    RFC 9110 section 15.6.3 - 502 Bad Gateway

    Internet Engineering Task Force · 2022 · official_doc

Sources: RFC 9110 section 15.6.3 - 502 Bad Gatewayreviewed 2026-08-22 · verified

Was this entry useful?