IIS : PHP output buffering not working

There is a way to set the Response Limit using the IIS Manager:

1. On the server main page, under “Management”, select “Configuration Editor”;
2. under “Section”, enter ‘system.webServer/handlers’;
3. next to “(Collection)” click “…” OR mark the element “(Collection)” and, under “Actions” und ‘(Collection)’ Element, click “Edit Items”;
4. scroll down until you find your PHP version under “Name”;
5. at the bottom, the Properties are shown an can be edited manually, including responseBufferLimit, which should be set to 0 for flush() to work.

The big Pro is that you can edit the properties for everything, not only PHP plus you can work with different versions (or even installations of the same version) of PHP.