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Flux generates black image in ComfyUI

The workflow completes but outputs black frames or images due to VAE, precision, scheduler, or model mismatch.

Error text / 报错原文

  • Flux black image
  • black image
  • NaN detected

What it means

The workflow completes but outputs black frames or images due to VAE, precision, scheduler, or model mismatch.

Most common causes

  • Wrong VAE
  • fp16 instability
  • Bad sampler settings
  • Model files incomplete

Fastest fix

  • Reproduce the smallest failing case.
  • Check environment, platform, and production settings.
  • Use the related local tool to classify the issue.
  • Fix the highest-risk security or data issue first.

Safe fix

  • Keep secrets out of client code and logs.
  • Prefer least privilege and explicit allowlists.
  • Add a regression test or checklist before retrying.
  • Document the working production configuration.

What not to do

  • Do not disable security controls as a permanent fix.
  • Do not paste secrets into public issue trackers or AI chats.
  • Do not trust preview success as production readiness.

Diagnostic commands

nvidia-smi
python -c "import torch; print(torch.cuda.is_available())"
python --version

Related tools

Related errors

Sources