🛠️ ComfyUI Troubleshooting Guide

Complete Solutions for Common Issues

Don't panic! Almost every ComfyUI issue has a simple fix. This guide walks you through solutions step-by-step.

📑 Quick Navigation

⚠️

Missing Models Dialog Appears

Severity: Low

🔍 What You See:

When you open ComfyUI, a dialog pops up saying "When loading the graph, the following models were not found" with a list of models and download buttons.

Example Message:
checkpoints / ltx-2-19b-distilled.safetensors
Download (40.31 GB)

🤔 Why This Happens:

ComfyUI automatically loads the last workflow you had open (or an example workflow). That workflow uses models you don't have downloaded yet.

This is completely normal and NOT an error! It's just letting you know what's missing from the workflow template.

✅ Solutions:

Option 1: Just Start Fresh (Recommended for Beginners)
  1. Click the X or "Don't show this again" to close the dialog
  2. Press Ctrl+A (select all) then Delete to clear the canvas
  3. Start building your own workflow with the models you have!
Option 2: Download the Missing Models

If you actually want to use that workflow:

  1. Click the Download button next to each model
  2. Wait for downloads to complete (some are 40GB+!)
  3. Models auto-install to /data/comfyui/models/
⚠️ Warning: Some models are HUGE (40GB+). Make sure you have enough space on /data (you have 655GB free).
Option 3: Load a Different Workflow
  1. Click Menu → Load (top left)
  2. Browse to a workflow that uses models you have
  3. Or use our Getting Started guide to build one from scratch!

🛡️ Prevent This Next Time:

  • Always save your own workflows: Menu → Save
  • Clear the canvas before closing ComfyUI if you don't want it to reload
  • Check "Don't show this again" if the dialog is annoying
🎮

GPU Not Detected / CUDA Errors

Severity: High

🔍 What You See:

  • Error message: "Can't initialize NVML"
  • Warning about CUDA capability
  • ComfyUI says "Device: cpu" instead of "Device: cuda:0"
  • Generation is EXTREMELY slow (5-10 minutes per image)
Console Output:
Device: cpu
VAE dtype: torch.float32
Using pytorch attention in VAE

🤔 Why This Happens:

  • NVIDIA drivers not installed or outdated
  • PyTorch not installed with CUDA support
  • GPU not passed through to VM (you're on a VM)
  • Another process is using the GPU

✅ Solutions:

Step 1: Check if GPU is Visible
# Run this command: nvidia-smi # Should show: # +-----------------------------------------------------------------------------+ # | NVIDIA-SMI 535.xx Driver Version: 535.xx CUDA Version: 12.x | # |-------------------------------+----------------------+----------------------+ # | GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC | # | 0 Quadro P5000 Off | 00000000:21:00.0 On | Off |
🚨 If nvidia-smi fails: Your GPU isn't accessible to the system. This is a driver or VM configuration issue.
Step 2: Verify CUDA PyTorch
# Check if PyTorch can see CUDA: cd ~/Book1-Production/ComfyUI ./venv/bin/python -c "import torch; print(f'CUDA available: {torch.cuda.is_available()}'); print(f'Device: {torch.cuda.get_device_name(0) if torch.cuda.is_available() else \"CPU\"}')" # Should print: # CUDA available: True # Device: Quadro P5000
Step 3: Fix NVIDIA Drivers (if nvidia-smi failed)
  1. Update GPU drivers:
    sudo ubuntu-drivers autoinstall sudo reboot
  2. After reboot, test again with nvidia-smi
Step 4: Reinstall PyTorch with CUDA (if torch.cuda.is_available() = False)
cd ~/Book1-Production/ComfyUI ./venv/bin/pip uninstall torch torchvision torchaudio -y ./venv/bin/pip install torch torchvision torchaudio --index-url https://download.pytorch.org/whl/cu121
Step 5: Restart ComfyUI
# Stop current instance pkill -f "python main.py" # Start fresh cd ~/Book1-Production/ComfyUI ./venv/bin/python main.py --listen 0.0.0.0 --port 8188
💡 Note about P5000: You'll see warnings about CUDA capability sm_61. This is normal! Your P5000 still works, it's just a bit older. Ignore these warnings - they don't affect functionality.
🐌

Very Slow Image Generation

Severity: Medium

🔍 What You See:

  • Generation takes 5+ minutes for a single 1024x1024 image
  • Progress bar moves incredibly slowly
  • System feels sluggish during generation
  • Each step takes 10-30 seconds

🤔 Why This Happens:

  • Running on CPU instead of GPU (see GPU issue above)
  • Too many steps in KSampler (50+ steps)
  • Image resolution too large (2048x2048+)
  • Multiple models loaded at once
  • VRAM full, causing swapping to system RAM

✅ Solutions:

⚡ Quick Fix: Lower your KSampler steps from 30 to 20, and reduce image size to 768x768. This can cut generation time in half!
Optimization Checklist:
  1. Verify GPU is being used
    # Should see GPU activity: watch -n 1 nvidia-smi
  2. Reduce steps in KSampler:
    • 30-25 steps: Good quality, reasonable speed
    • 20 steps: Faster, still good for testing
    • 15 steps: Very fast, lower quality
  3. Use smaller image sizes:
    • 1024x1024: Standard SDXL (30-60 sec)
    • 768x768: Faster (20-40 sec)
    • 512x512: Very fast (10-20 sec)
  4. Close other GPU applications:
    # Check what's using GPU: nvidia-smi # Kill other GPU processes if needed
  5. Use appropriate sampler:
    • Fast: dpmpp_2m, dpmpp_2m_sde
    • Slower but better: euler_ancestral, dpm_2
💡 Expected Times on P5000:
  • 1024x1024, 25 steps: ~30-60 seconds
  • 768x768, 20 steps: ~20-30 seconds
  • 512x512, 20 steps: ~10-15 seconds
If yours is slower, check if GPU is actually being used!
💾

Out of Memory / CUDA OOM Errors

Severity: High

🔍 What You See:

  • Error: "CUDA out of memory"
  • Error: "RuntimeError: cuDNN error: CUDNN_STATUS_NOT_INITIALIZED"
  • Generation starts but crashes halfway through
  • ComfyUI freezes or becomes unresponsive
Error Message:
RuntimeError: CUDA out of memory. Tried to allocate 1.95 GiB
(GPU 0; 15.78 GiB total capacity; 13.24 GiB already allocated)

🤔 Why This Happens:

  • Image resolution too large for available VRAM
  • Multiple models loaded simultaneously
  • Batch size too high (generating multiple images at once)
  • VRAM not clearing between generations
  • Other applications using GPU

✅ Solutions:

⚡ Quick Fix: Close ComfyUI browser tab, wait 30 seconds for VRAM to clear, then reload. Reduce image size or batch size before trying again.
Immediate Fixes:
  1. Clear VRAM:
    # Stop ComfyUI pkill -f "python main.py" # Wait for GPU to clear sleep 10 # Restart cd ~/Book1-Production/ComfyUI ./venv/bin/python main.py --listen 0.0.0.0 --port 8188
  2. Reduce Image Resolution:
    • Try 768x768 instead of 1024x1024
    • Or 512x512 for testing
  3. Lower Batch Size:
    • In Empty Latent Image node, set batch_size to 1
  4. Change VRAM Settings:
    • In ComfyUI, go to Settings
    • Find "Enable low VRAM mode" or "VAE in CPU"
    • Enable these to use less VRAM
  5. Close other GPU applications:
    # Check what's using VRAM: nvidia-smi # Example output showing usage: # | 0 Quadro P5000 On | 00000000:21:00.0 Off | Off | # | 0% 52C P8 14W / 180W | 13245MiB / 16260MiB | 0% Default |
Long-term Solution: Start ComfyUI with Low VRAM Mode
cd ~/Book1-Production/ComfyUI ./venv/bin/python main.py --listen 0.0.0.0 --port 8188 --lowvram
💡 What --lowvram does: Moves models between VRAM and system RAM as needed. Slightly slower, but prevents crashes.

🛡️ Prevent OOM Errors:

  • Don't exceed 1024x1024 resolution on P5000
  • Keep batch_size at 1 unless you specifically need multiple images
  • Close unused browser tabs with ComfyUI open
  • Monitor VRAM with: watch -n 2 nvidia-smi
🔗

Nodes Won't Connect Together

Severity: Low

🔍 What You See:

  • Can't drag a line between two nodes
  • Line appears but disappears when you release
  • Connection doesn't "stick"
  • Red error appears when trying to connect

🤔 Why This Happens:

  • Incompatible types: You're trying to connect outputs that don't match inputs
  • Wrong direction: Connecting input-to-input or output-to-output
  • Slot already occupied: Some inputs only accept one connection

✅ Solutions:

Understanding Node Connections:
Connection Rules:
  • Left side = Inputs (where data comes IN)
  • Right side = Outputs (where data goes OUT)
  • Colors indicate types:
    • Purple = MODEL
    • Yellow = CONDITIONING
    • Pink = LATENT
    • Blue = IMAGE
    • Orange = CLIP
    • Red = VAE
Common Connection Mistakes:
  1. Wrong direction:
    • ❌ Input → Input (won't work)
    • ❌ Output → Output (won't work)
    • ✅ Output → Input (correct!)
  2. Type mismatch:
    • ❌ Connecting LATENT output to IMAGE input
    • ✅ Use VAE Decode to convert LATENT → IMAGE first
  3. Already connected:
    • Most inputs only accept ONE connection
    • To change: disconnect first, then connect new one
How to Properly Connect:
  1. Click and hold on an output dot (right side of node)
  2. Drag to an input dot (left side of another node)
  3. Release when you see the dot highlight
  4. A line should appear connecting them
💡 Pro Tip: Hover over a connection dot to see its type. ComfyUI will show you what it expects (e.g., "model (MODEL)" or "images (IMAGE)").
🔴

Red Nodes / Error Messages in Workflow

Severity: High

🔍 What You See:

  • Node has red background or red border
  • Error text appears in the node
  • Can't queue the workflow
  • "Required input is missing: XXX" message

🤔 Why This Happens:

  • Missing connections: Required inputs aren't connected
  • Missing model: Selected checkpoint/model doesn't exist
  • Invalid settings: Parameter values are out of range
  • Custom node not installed: Workflow uses nodes you don't have

✅ Solutions:

Step 1: Read the Error Message
Error appears in the node or console:
"Required input is missing: model"
"Checkpoint 'model_name.safetensors' not found"
"Node type 'CustomNode' not found"
Step 2: Fix Based on Error Type
Error: "Required input is missing"
  1. Look at the node - which input is empty?
  2. Connect the required input from another node
  3. Red should turn back to normal
Error: "Checkpoint not found"
  1. Click the dropdown in the node
  2. Select a model you actually have (like sd_xl_base_1.0.safetensors)
  3. Or download the missing model
Error: "Node type not found"
  1. This workflow uses a custom node you don't have
  2. Go to ComfyUI Manager (if installed)
  3. Search for and install the missing custom node
  4. Restart ComfyUI after installation
Error: "Invalid value for parameter"
  1. Check the parameter value in the node
  2. Common issues:
    • Negative numbers where only positive allowed
    • Text in a number field
    • Value outside allowed range
  3. Reset to default or enter valid value
💡 Debug Tip: Right-click the red node → Properties to see detailed error info. This often tells you exactly what's wrong!
🖼️

Can't Find My Generated Images

Severity: Low

🔍 What You See:

  • Generation completes successfully
  • Image shows in ComfyUI preview
  • But can't find the file anywhere
  • Don't know where images are saved

✅ Solutions:

⚡ Your images are saved to: /data/comfyui/output/
How to Access Your Images:
  1. Via Terminal:
    # View your generated images: ls -lh /data/comfyui/output/ # Open the folder in file manager: nautilus /data/comfyui/output/
  2. Via ComfyUI Interface:
    • Click the image in the Save Image node
    • It will open in a preview
    • Right-click the preview → Save Image
  3. Change Save Location:
    • In Save Image node, change "filename_prefix"
    • Example: my-art/dragon_ will save to /data/comfyui/output/my-art/
Understanding Filenames:
Default filename format:
ComfyUI_00001_.png
ComfyUI_00002_.png

With custom prefix "dragon":
dragon_00001_.png
dragon_00002_.png
Create Easy Access:
# Create a symlink in your home folder: ln -s /data/comfyui/output ~/ComfyUI-Output # Now you can access images at: # ~/ComfyUI-Output/
💡 Organizing Tip: Use descriptive filename prefixes like "characters/elf_", "landscapes/mountain_", etc. to keep your work organized!
⬛

Output is Blank or All Black

Severity: Medium

🔍 What You See:

  • Generation completes without errors
  • Output image is completely black
  • Or output is blank/white
  • Or output is just noise/static

🤔 Why This Happens:

  • Wrong VAE connected or missing: VAE not properly wired
  • Denoising set wrong: denoise = 0 means no generation
  • Steps too low: Not enough steps to form image
  • Model not loaded properly: Checkpoint failed to load
  • Seed issue: Extremely unlucky seed

✅ Solutions:

  1. Check VAE Connection:
    • Make sure Load Checkpoint's VAE output connects to VAE Decode
    • VAE Decode should connect to Save Image
  2. Check Denoise Value:
    • In KSampler, denoise should be 1.0 for fresh generation
    • denoise = 0 means "change nothing" = blank
  3. Increase Steps:
    • KSampler steps should be at least 20
    • Try 25-30 for good quality
  4. Try Different Seed:
    • In KSampler, click "control_after_generate" dropdown
    • Select "randomize"
    • Generate again
  5. Reload Checkpoint:
    • In Load Checkpoint, re-select the model from dropdown
    • Look in console for errors like "failed to load"
Workflow Sanity Check:
Your workflow should look like:
Load Checkpoint → CLIP → CLIP Text Encode (Positive)
↓ CLIP → CLIP Text Encode (Negative)
↓ MODEL → KSampler
↓ VAE → VAE Decode

Empty Latent → KSampler → VAE Decode → Save Image
📂

Can't Load Saved Workflow

Severity: Medium

🔍 What You See:

  • Try to load workflow, nothing happens
  • Error: "Failed to load workflow"
  • Workflow loads but nodes are missing
  • Workflow loads but all nodes are red

🤔 Why This Happens:

  • Workflow uses custom nodes you don't have installed
  • Workflow file is corrupted
  • Wrong file format (.png vs .json)
  • ComfyUI version mismatch

✅ Solutions:

Method 1: Load JSON Workflow
  1. Make sure file is .json format
  2. Click Menu → Load
  3. Browse to your workflow file
  4. Click Open
Method 2: Load from PNG (if workflow was saved as image)
  1. Drag the PNG file onto the ComfyUI canvas
  2. OR: Menu → Load → select the PNG
  3. Workflow should extract from image metadata
If Workflow Uses Missing Custom Nodes:
  1. Open ComfyUI Manager (gear icon in sidebar, if installed)
  2. Go to "Install Missing Nodes"
  3. Click "Install" next to missing nodes
  4. Restart ComfyUI after installation
  5. Try loading workflow again
⚠️ If workflow still won't load: It might be from a much newer/older version of ComfyUI and may need manual reconstruction.
🔌

WebSocket Connection Failed

Severity: Medium

🔍 What You See:

  • Error in browser console: "WebSocket connection failed"
  • Queue button doesn't work
  • No real-time preview during generation
  • Interface feels disconnected/unresponsive

🤔 Why This Happens:

  • HTTPS accessing WS: Secure page trying to use insecure WebSocket
  • Proxy misconfiguration: Traefik not passing WebSocket headers
  • Firewall blocking: Port 8188 WebSocket connections blocked
  • ComfyUI not running: Server crashed or not started

✅ Solutions:

  1. Check ComfyUI is Running:
    ps aux | grep "python main.py" # Should show running process
  2. Access Directly (bypass proxy):
    • Try: http://192.168.50.138:8188
    • If this works, it's a proxy issue
  3. Check Browser Console:
    • Press F12 to open Developer Tools
    • Go to Console tab
    • Look for specific WebSocket errors
    • Note the URL it's trying to connect to
  4. Restart ComfyUI with CORS enabled:
    cd ~/Book1-Production/ComfyUI ./venv/bin/python main.py --listen 0.0.0.0 --port 8188 --enable-cors-header
💡 For your setup: Since you're accessing via comfyui.richeyda.com, make sure Traefik's WebSocket middleware is properly configured. The connection should work fine on local network (192.168.50.138:8188).
📦

Missing Dependencies (cv2, imageio, etc.)

Severity: Low

🔍 What You See:

  • Error: "ModuleNotFoundError: No module named 'cv2'"
  • Error: "No module named 'imageio_ffmpeg'"
  • Custom nodes show "IMPORT FAILED" in console
  • Specific features don't work (video, ControlNet Aux)
Console Error:
Cannot import /data/comfyui/custom_nodes/ComfyUI-VideoHelperSuite module for custom nodes: No module named 'cv2'
Cannot import /data/comfyui/custom_nodes/comfyui_controlnet_aux module for custom nodes: No module named 'cv2'

🤔 Why This Happens:

  • Python packages not installed: Required dependencies missing from venv
  • Custom nodes need extra packages: Node didn't auto-install requirements
  • System libraries missing: Some packages need system-level dependencies

✅ Solutions:

Install Missing Python Packages:
cd ~/Book1-Production/ComfyUI # For cv2 (OpenCV) - needed for video and ControlNet: ./venv/bin/pip install opencv-python # For video features: ./venv/bin/pip install imageio-ffmpeg # For face restoration: ./venv/bin/pip install facexlib # Install all at once: ./venv/bin/pip install opencv-python imageio-ffmpeg facexlib
After Installing, Restart ComfyUI:
# Stop current instance pkill -f "python main.py" # Start fresh ./venv/bin/python main.py --listen 0.0.0.0 --port 8188
Check if Dependencies Loaded Successfully:
# Look in the startup log: # Should no longer see "IMPORT FAILED" for those nodes # Check specific import: ./venv/bin/python -c "import cv2; print('OpenCV version:', cv2.__version__)"
✅ What This Enables:
  • opencv-python: Video processing, ControlNet Aux nodes
  • imageio-ffmpeg: Video export/import
  • facexlib: Face restoration and enhancement
💡 Note: ComfyUI core works fine without these! They're only needed for specific custom nodes/features.
🚫

ComfyUI Won't Start / Crashes on Launch

Severity: Critical

🔍 What You See:

  • Run command, but nothing happens
  • ComfyUI starts then immediately crashes
  • Error: "Address already in use"
  • Python errors during startup

✅ Solutions by Error Type:

Error: "Address already in use" (Port 8188 busy)
# Find what's using port 8188: sudo netstat -tulpn | grep 8188 # OR use lsof: sudo lsof -i :8188 # Kill the process: pkill -f "python main.py" # Try starting again: cd ~/Book1-Production/ComfyUI ./venv/bin/python main.py --listen 0.0.0.0 --port 8188
Error: Python/Module Import Errors
# Reinstall dependencies: cd ~/Book1-Production/ComfyUI ./venv/bin/pip install --upgrade torch torchvision torchaudio --index-url https://download.pytorch.org/whl/cu121 ./venv/bin/pip install -r requirements.txt # If virtual env is corrupted, recreate it: rm -rf venv python3 -m venv venv ./venv/bin/pip install -r requirements.txt
Error: CUDA/GPU Related Startup Crash
# Start with CPU mode (slower but tests if GPU is the issue): ./venv/bin/python main.py --listen 0.0.0.0 --port 8188 --cpu # If that works, GPU drivers need attention
ComfyUI Starts But Immediately Crashes:
  1. Check the console output for error messages
  2. Look in: /data/comfyui/user/comfyui.log
  3. Common causes:
    • Corrupted model file
    • Bad custom node
    • Permission issues with /data/comfyui folders
Nuclear Option: Fresh Start (if nothing else works)
⚠️ WARNING: This removes all custom nodes and settings!
cd ~/Book1-Production/ComfyUI # Backup first! cp -r custom_nodes custom_nodes.backup cp -r user user.backup # Remove problematic custom nodes: rm -rf custom_nodes/* # Keep only ComfyUI-Manager: # (manually restore it from backup if you want) # Restart: ./venv/bin/python main.py --listen 0.0.0.0 --port 8188
🎨

Poor Quality / Weird-Looking Results

Severity: Low

🔍 What You See:

  • Images are blurry or low detail
  • Colors are washed out
  • Weird artifacts or distortions
  • Results don't match prompt
  • Images look "AI-generated" in a bad way

✅ Solutions:

Improve Your Prompts:
❌ Weak Prompt:
"a dragon"
✅ Strong Prompt:
"majestic dragon with scales, flying over snowy mountains at sunset, fantasy art, highly detailed, dramatic lighting, 8k, masterpiece"
Use Better Negative Prompts:
Common negative prompt for quality: "blurry, low quality, distorted, ugly, bad anatomy, bad hands, deformed, mutated, watermark, signature, text, cropped, worst quality, jpeg artifacts"
Adjust KSampler Settings:
  • Steps: Increase to 30-35 for better quality (slower)
  • CFG Scale:
    • Too low (3-5): Ignores prompt, creative but random
    • Sweet spot (7-9): Balanced
    • Too high (15+): Over-saturated, artifacts
  • Sampler: Try different ones:
    • euler_ancestral: Good for variety
    • dpmpp_2m_karras: Good quality/speed
    • dpm_2: High quality, slower
Use Correct Resolution:
⚠️ SDXL trained on 1024x1024! Using other sizes (like 512x512) will produce lower quality.
Add an Upscaler:
  • After generation, add Upscale Image node
  • Use RealESRGAN_x4plus model
  • Takes your 1024x1024 → 4096x4096 with better detail
💡 Pro Tip: Quality is 80% prompt, 15% settings, 5% luck. Invest time in learning good prompt engineering!
🧩

Custom Nodes Won't Install

Severity: Medium

🔍 What You See:

  • Try to install custom node, fails
  • Git clone errors
  • Node installs but doesn't appear in menu
  • Import errors after installation

✅ Solutions:

Method 1: Install via ComfyUI Manager (Easiest)
  1. Open ComfyUI Manager (gear icon in sidebar)
  2. Go to "Install Custom Nodes"
  3. Search for the node you want
  4. Click "Install"
  5. Restart ComfyUI when done
Method 2: Manual Git Clone
cd ~/Book1-Production/ComfyUI/custom_nodes # Clone the custom node repo: git clone https://github.com/username/custom-node-name # Install its dependencies: cd custom-node-name ../../venv/bin/pip install -r requirements.txt # Go back and restart ComfyUI: cd ~/Book1-Production/ComfyUI ./venv/bin/python main.py --listen 0.0.0.0 --port 8188
If Installation Fails:
  1. Check error message - often says what's wrong
  2. Permission issues:
    # Fix ownership: sudo chown -R kubuntu:kubuntu /data/comfyui/custom_nodes
  3. Git not installed:
    sudo apt install git
  4. Dependencies conflict:
    • Some custom nodes have conflicting requirements
    • Try installing them one at a time
    • Check custom node's GitHub issues for known problems
Node Installed But Doesn't Appear:
  1. Make sure you restarted ComfyUI after installation
  2. Check console for import errors during startup
  3. Try: Right-click canvas → refresh to rebuild node menu

🆘 Still Having Issues?

If none of these solutions helped:

  1. Check ComfyUI logs: /data/comfyui/user/comfyui.log
  2. Look in browser console (F12) for errors
  3. Check ComfyUI GitHub Issues: github.com/comfyanonymous/ComfyUI/issues
  4. Visit r/comfyui on Reddit for community help
  5. Check your systemd service logs: journalctl -u comfyui -f
🔍 Debugging Commands Cheat Sheet:
# Check if ComfyUI is running: ps aux | grep "python main.py" # Check GPU: nvidia-smi # View logs: tail -f /data/comfyui/user/comfyui.log # Test PyTorch + CUDA: cd ~/Book1-Production/ComfyUI ./venv/bin/python -c "import torch; print(torch.cuda.is_available())" # Check port 8188: sudo netstat -tulpn | grep 8188 # Restart ComfyUI: pkill -f "python main.py" cd ~/Book1-Production/ComfyUI ./venv/bin/python main.py --listen 0.0.0.0 --port 8188