How to prepare your website for a PHP upgrade

A PHP upgrade moves your website to a newer version of PHP, the programming language that WordPress and many other sites run on. If your theme, plugins and custom code support the new version, your visitors will not notice a thing and your site gets security updates again. So before you switch, update your software, make a backup and test the new version on a copy of your site. This guide walks you through each step and tells you what to check once the switch is done.

Why does your website need a newer PHP version?

Every PHP version is supported for four years: two years of full support, then two years of security fixes only. After that the version reaches end of life, and new vulnerabilities in it are no longer fixed. PHP 8.2, for example, gets no security updates after 31 December 2026. For the support dates of every version, see the table in how to change the PHP version in Plesk.

Your software moves on as well. More and more plugins and themes require a recent PHP version. When an update needs a newer version than your site runs, WordPress shows "This update does not work with your version of PHP" and does not install it. Site Health warns you with "Your site is running on an outdated version of PHP" as soon as your version no longer receives security updates.

Minor update or a new PHP version?

PHP updates come in two kinds. A PHP upgrade, which is what this guide is about, is always the second kind.

What changes for your website?

If all your software works with the new version, your site looks exactly the same after the switch, and newer PHP versions are often faster too. The switch itself takes a few seconds; on some of our servers your site is unavailable during those seconds.

Trouble comes from code written the old way: a plugin or theme that has not been updated for years, an old page builder or custom code. You will notice it in one of these ways:

• A blank page, a 500 error or the message "There has been a critical error on this website." WordPress also emails the site administrator with the subject "Your Site is Experiencing a Technical Issue". That email contains a recovery mode link that still gets you into your dashboard.
• A page that loads but is missing something, such as page builder content, a slider, a form or the footer. There is no error message for this, so look closely at the content of your key pages after the switch.
• An error on a single screen, for example a plugin's settings page in your dashboard, while the rest of your site works.
• "Deprecated" messages in the error log. These warn that a piece of code will stop working in a later PHP version. Your site still works, and an update of that plugin or theme usually clears them.

With LJPc hosting, error messages go to the error log rather than onto your pages, so visitors never see them. To open and read that log, see how to view error logs in Plesk.

Two things do not follow the new version on their own: a scheduled task of the type Run a PHP script keeps its own PHP version, and PHP settings marked (Default) take the default value of the new version. Both are part of the checks after the switch.

What to check before you upgrade

1. Find out which PHP version your site runs now. In Plesk it is shown on your domain card under Dev Tools, next to PHP. In WordPress, go to Tools > Site Health > Info and open Server.
2. Update WordPress, your theme and your plugins. Developers adapt their software to new PHP versions, so the latest releases prevent most problems. For a safe way to do this, see how to update WordPress safely.
3. Look for outdated components. On a plugin's page on wordpress.org, Last updated tells you how recent it is and PHP version shows the minimum version it needs. A plugin or theme that has not been updated for years, or that is no longer listed, is the most likely to break. For a premium plugin or theme, check the developer's site for the PHP versions they support. If a developer built custom code for you, ask whether it has been tested on the new version.
4. Make a backup of your files and database, as described in how to make a website backup.
5. Test the new version on a copy. Use WP Toolkit to create a staging copy on a subdomain such as staging.yourdomain.com. A subdomain has its own PHP version in Plesk, so you switch only the copy to the new version and run the checks below on it. See how to create a WordPress staging site.

Switch yourself when it suits you

You choose your site's PHP version yourself in Plesk, under Dev Tools > PHP. That way you decide when the switch happens, for example at a quiet moment when you can check your site straight away. If we have told you about an upcoming PHP upgrade, you can pick the new version earlier yourself. Choose the newest version your software supports; WordPress itself recommends PHP 8.3 or higher. The steps are in how to change the PHP version in Plesk.

After the switch: how to check your site

1. Clear the cache of your caching plugin, if you use one. Otherwise you will see a page that was stored before the switch.
2. View your key pages as a visitor, ideally in a private window: your homepage, your service or product pages and your contact page. Check that every part of the page is still there, not only that it loads.
3. Test what your visitors do. Submit a form, and in a webshop place an order up to the payment step.
4. Log in to your dashboard and open the settings of the plugins you use.
5. Check the error log for new lines with PHP Fatal error.
6. Check your scheduled tasks under Scheduled Tasks and give any Run a PHP script task the same version as your site. To edit a task, see how to set up cron jobs in Plesk.
7. Check your PHP settings, such as memory_limit and upload_max_filesize. What each setting does is explained in how to change PHP settings in Plesk.

Site broken after the PHP upgrade?

1. Find the plugin or theme behind the error in the error log. The path in the message points to it, for example wp-content/plugins/plugin-name/.
2. Update that plugin or theme. If there is no update, deactivate the plugin and pick a maintained alternative. If you cannot reach your dashboard, use the recovery mode link from the WordPress email.
3. Switch back temporarily if needed to the previous PHP version, as long as it is still listed under PHP version. Treat that as a delay, not a fix: a version without security updates is no lasting solution, and PHP 8.1 and older can no longer be selected on our servers.

What LJPc hosting takes care of

• Minor PHP updates with bug and security fixes are installed automatically on all our servers. You do not need to do anything for those.
• You choose the PHP version per website and per subdomain: 8.2, 8.3, 8.4 and, on almost all our servers, 8.5.

Would you like help preparing, testing or fixing an error after the switch? Call us on +31 85 130 6429, email support@ljpc.nl or create a support ticket.