How to Fix HTTP Errors in WordPress: 404, 500, 502, 503, 504

WordPress sites generate distinctive error patterns: 404 from broken permalinks, 500 from plugin/theme conflicts and PHP errors, 502 from PHP-FPM or upstream issues, 503 from maintenance mode stuck or memory exhaustion, 504 from slow queries or external API timeouts. This guide covers the WordPress-specific diagnosis-and-fix workflow per error. Pair with HTTP error guide.

Step 1: Enable WordPress debug logging

Edit wp-config.php: define('WP_DEBUG', true); define('WP_DEBUG_LOG', true); define('WP_DEBUG_DISPLAY', false). Errors log to /wp-content/debug.log. Critical first step — diagnosis without logs is guessing.

Step 2: Diagnose 404 errors

Check Settings → Permalinks → click Save (re-flushes rewrite rules — fixes most 404s). For broken inbound links, install Redirection plugin to catch and 301 them. Update internal links pointing to dead URLs.

Step 3: Diagnose 500 errors

Look at debug.log for PHP fatal errors. Common causes: plugin update broke compatibility, theme conflict, exhausted memory limit, corrupted .htaccess. Disable all plugins via /wp-content/plugins rename, re-enable one by one to identify culprit.

Step 4: Diagnose 502/504 errors

Server-level errors. Check PHP-FPM status (managed hosts have logs). Often caused by: long-running queries, external API timeouts, exhausted PHP workers. Increase PHP timeout (php.ini max_execution_time), increase memory_limit, kill stuck queries via Query Monitor or hosting dashboard.

Step 5: Diagnose 503 errors

WordPress 'Briefly unavailable for scheduled maintenance' page that doesn't go away: delete .maintenance file from root via FTP. True 503 (server-level): check hosting account for resource limits hit. Increase plan or optimise resource-heavy plugins.

Step 6: Fix memory limit issues

WordPress 'Allowed memory size exhausted' messages. wp-config.php: define('WP_MEMORY_LIMIT', '256M');. If still failing on admin actions: define('WP_MAX_MEMORY_LIMIT', '512M');. If host caps below this, contact host or upgrade plan.

Step 7: Set up monitoring

Uptime Robot, Better Uptime, or hosting-built-in monitoring. Alert on 5xx errors immediately. Track 404 rate via Search Console; spikes indicate broken links or removed pages.

Frequently Asked Questions

What does 'White Screen of Death' mean in WordPress?

A 500 error where PHP errors aren't displayed because WP_DEBUG_DISPLAY is off. The site appears blank. Enable debug logging immediately (wp-config.php), then look at debug.log. Common causes: plugin conflict after update, theme function calling undefined function, memory limit hit during heavy operation.

Why am I getting 504 timeout errors on the admin?

WordPress admin operations (especially bulk actions, plugin updates, theme changes) can exceed PHP execution time. Increase max_execution_time in php.ini to 300s, and increase WP_MAX_MEMORY_LIMIT. For very slow operations consider using WP-CLI from SSH instead of the admin UI.

How do I fix 404s after migrating WordPress?

First: Settings → Permalinks → Save (re-generates .htaccess rules). If still failing on existing URLs, check .htaccess for outdated rewrite rules. For URL changes (slugs renamed), install Redirection plugin and add 301s from old to new.

Will increasing PHP memory limit slow down my site?

No, it allows operations to use more memory if needed. Memory limit isn't pre-allocated. Higher memory limits enable larger imports, complex queries, and plugin updates without crashing.

Why does my WordPress site randomly show 502 errors?

PHP-FPM worker exhaustion. Your server has a fixed number of PHP workers; each request consumes one. If requests are slow (database queries, external APIs), workers stay busy and new requests get 502. Solutions: faster queries (database optimisation), reduced external API calls, increased PHP workers (server config), or caching to bypass PHP entirely.

🔍 Audit your WordPress HTTP errors

Find 4xx and 5xx errors across your site.

Run HTTP Error Audit →