n8n Connection Error Diagnosis & Resolution

Deterministic diagnostic guide for all n8n v1.x connection failures. Format: Symptom -> Cause -> Fix. ALWAYS follow the diagnostic tables.

Quick Reference: Connection Error Categories

Category	Common Symptom	Go To
API connection	HTTP 4xx/5xx, ECONNREFUSED, ETIMEDOUT	API Failures
Credentials	401 Unauthorized, 403 Forbidden	Credential Errors
Timeouts	ETIMEDOUT, ESOCKETTIMEDOUT, execution hangs	Timeout Configuration
SSL/TLS	UNABLE_TO_VERIFY_LEAF_SIGNATURE, CERT_HAS_EXPIRED	SSL/TLS Errors
Webhooks	Webhook not triggering, 404 on webhook URL	Webhook URL Issues
Rate limiting	429 Too Many Requests	Rate Limiting
Queue mode	Redis ECONNREFUSED, worker not picking up jobs	Queue Mode (Redis)
Database	ECONNREFUSED on 5432, SQLite SQLITE_BUSY	Database Errors