Fix Critical Error in WordPress

You hit a white screen that says “There has been a critical error on this website.” Maybe you also got an email from WordPress about recovery mode. This is WordPress 5.2+‘s fatal error handler catching a PHP error that would otherwise crash your site completely. The good news: your data is fine. The bad news: something in your code is broken and you need to find it.

What Causes Critical Error?

Plugin conflict or broken update — A plugin updated and now throws a fatal PHP error. This is the cause about 70% of the time.
Theme incompatibility — Your theme requires a PHP version or WordPress version you don’t have, or a theme update introduced a bug.
PHP version mismatch — Your host upgraded PHP and a plugin hasn’t caught up. Old plugins calling deprecated functions will crash hard on PHP 8.x.
Exhausted memory limit — WordPress ran out of the memory PHP allocated to it, usually during a heavy operation.
Corrupted core files — Rare, but a failed WordPress core update can leave files in a half-written state.

How to Fix It

Step 1: Check the Recovery Mode Email

WordPress sends a recovery mode email to the admin address on file. Open it and click the recovery mode link — this gives you temporary admin access even while the site is down.

If you never got the email, check your spam folder. If it’s not there, skip to Step 2 — you’ll fix this from the server side.

Step 2: Enable Debug Logging

Connect to your site via FTP/SFTP or your host’s File Manager. Open wp-config.php in the root directory and find the line that says That's all, stop editing!. Add these lines above it:

define( 'WP_DEBUG', true );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );

Setting WP_DEBUG_DISPLAY to false keeps errors out of your HTML output — the right way to do this on a live site. Errors go to wp-content/debug.log instead.

Reload the broken page, then open wp-content/debug.log via FTP. The last few lines will tell you exactly which file triggered the fatal error. You’ll see something like:

PHP Fatal error: Uncaught Error: Call to undefined function some_function()
in /home/yoursite/public_html/wp-content/plugins/broken-plugin/includes/class-main.php on line 42

That file path tells you whether it’s a plugin or theme issue.

Step 3: Deactivate the Problem Plugin

If the debug log points to a plugin, rename its folder via FTP to deactivate it instantly:

Navigate to wp-content/plugins/ and rename the offending plugin folder. For example:

wp-content/plugins/broken-plugin → wp-content/plugins/broken-plugin-disabled

If you have WP-CLI access (and you should — skip this if you want headaches later with manual FTP every time something breaks):

wp plugin deactivate broken-plugin

If you’re not sure which plugin is the problem, deactivate them all:

wp plugin deactivate --all

Then reactivate one at a time until the error returns. That’s your culprit.

Step 4: Switch to a Default Theme

If the debug log points to your theme, switch to a default theme via FTP. Rename your active theme’s folder in wp-content/themes/:

wp-content/themes/your-theme → wp-content/themes/your-theme-disabled

WordPress will fall back to the latest default theme (Twenty Twenty-Five). Or with WP-CLI:

wp theme activate twentytwentyfive

Step 5: Increase the PHP Memory Limit

If the debug log shows Allowed memory size exhausted, bump the limit in wp-config.php:

define( 'WP_MEMORY_LIMIT', '256M' );

You may also need to set it in your .htaccess file:

php_value memory_limit 256M

Or in php.ini if your host allows it:

memory_limit = 256M

256M is plenty for most sites. If you need more than that, you have a plugin with a memory leak — find it and replace it.

Step 6: Reinstall WordPress Core

If none of the above works, core files may be corrupted. WP-CLI makes this painless:

wp core download --skip-content --force

This replaces all core files without touching wp-content/ — your themes, plugins, and uploads stay intact. If you don’t have WP-CLI, download a fresh copy of WordPress from wordpress.org, extract it, and upload everything except the wp-content folder via FTP.

After fixing the issue, go back to wp-config.php and disable debug mode:

define( 'WP_DEBUG', false );

Don’t leave debug logging on in production. It writes to disk on every page load and the log file grows until it eats your storage.

Prevention

Stage updates before applying them to production. Use a staging environment (most managed hosts like Kinsta and SiteGround offer one-click staging) to test plugin and theme updates before pushing live.
Keep PHP current and test compatibility. When your host offers a PHP upgrade, test it on staging first. Check the WordPress plugin compatibility checker or the plugin’s changelog for PHP version support.
Use a site health monitor. The built-in Tools → Site Health screen flags outdated PHP, plugin conflicts, and memory issues before they become critical errors.
Maintain WP-CLI access. When your admin dashboard is locked out, WP-CLI is the fastest way to diagnose and fix issues from the command line. Ask your host to enable it if it’s not already available.

Last verified: April 2026

Symptoms