How to Fix the WordPress Theme Customizer Not Working Error

The theme customizer is where the real action of editing all aspects of your website takes place. However, in some situations, the WordPress theme customizer may stop working and display a blank screen.

While it’s normal to panic, let me reassure you that this is one of the common WordPress errors that can be fixed. The following steps will help you troubleshoot the WordPress theme customizer not loading error effectively and quickly.

Let’s get going.

What is the theme customizer not working error?

The error occurs when you try to access the WordPress theme customizer under the Appearance tab. The customizer stops working and you see a blank screen like the one below.

WordPress theme customizer not working error

There could be different reasons behind this error. Let us go through the different solutions to the error.

1. Clear the browser and site cache

The first and simplest solution is to clear your browser cache. It could be that some scripts that are stored in your browser cache are blocking the WordPress customizer from loading. Clearing the cache will help to render the customizer properly.

Along with this, you should also clear your website cache. Clearing the site cache will be useful if you’ve turned on caching for logged-in users as well.

2. Switch to the default theme

There could be a problem with your current theme that is interfering with the loading of the theme customizer. To rule out this possibility, try switching to the default WordPress theme.

You can change themes by navigating to Appearance > Themes in your WordPress dashboard.

Did switching over help rectify the problem? If not, try the next solution.

3. Disable all the plugins

One of the plugins installed on your website could also be interfering with the proper loading of the customizer due to some script running in the background. To check plugin-related matters, you should disable all the plugins on your site.

Then try to access the theme customizer. If the customizer now loads correctly, it means that one of the plugins was causing the error. Now, activate the plugins one by one, each time checking whether the customizer is working or not.

This way you can identify the rogue plugin before long.

4. Update PHP version

Since WordPress is powered by PHP, it’s possible that outdated PHP script running on your server could be the reason behind the customizer not loading issue.

To check the PHP version running on your site, navigate to Tools > Site Health > Info > Server.

WordPress PHP version

If the PHP version is lower than 7.0, you need to upgrade it ASAP. You should be able to update the PHP version from your hosting panel. If you can’t, you should ask your web host to upgrade the PHP, preferably, to the latest version.

5. Update WordPress and the current theme

I also recommend that you’re using the latest version of WordPress. If not, you should update it immediately as recently version 5.9 was released that introduced full site editing, and the customizer was replaced with the Site Editor for WordPress block themes.

In addition to updating the core, you should also update your current theme to the latest version and also make sure that the theme is regularly updated by the theme author since legacy themes use outdated code that could also interfere with the smooth rendering of the theme customizer.

6. Replace the wp_ob_end_flush_all function

If none of the above solutions worked for fixing the theme customizer loading problem, then copy and paste the following code in the functions.php file of your current theme.

remove_action( 'shutdown', 'wp_ob_end_flush_all', 1 );
add_action( 'shutdown', function() {
   while ( @ob_end_flush() );
} );


Hopefully, one of the solutions mentioned here worked in resolving the WordPress theme customizer not loading problem on your website. However, in the rare case it didn’t, please don’t hesitate to reach out to our professional WordPress error fixing service where we troubleshoot all WordPress errors quickly and reliably.

About Trishan Mehta

Trishan Mehta is a WordPress fanatic since 2009. When not WordPressing, he is busy exploring hidden natural getaways whenever he can grab an opportunity. You can grab his WordPress SEO eBook to get up to speed with WordPress SEO.

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