Do i have to remove the entire casing to replace my timer on my greenstar 28i junior? If not how does it pop out please?

Gina, February 2017

You do have to remove the cover. See the installation guide.

All these links are what YOU should have been able to find with YOUR search:

https://www.worcester-bosch.co.uk/support/document/download/release/8716115166/12640

Is this an MT10 timer?

http://www.diynot.com/diy/threads/mt10-timer-failed-on-worcester-greenstar-28i-junior.338440/

https://www.worcester-bosch.co.uk/professional/support/documents/worcester-mt10-installation-instructions

Anon, February 2017