cylinder size

Just found our that my front door to my flat can be opened with another key, screwdriver or pretty much anything. I need to replace the cylinder, (Landlord's on holiday)found some on ebay but stuck on sizes to purchase, any help appreciated...

Hi all, We're about to have a new heating system installed (previous thread for a bit of history: https://www.diynot.com/diy/threads/too-many-boilers-for-the-22mm-pipe.511647/ ) Most of the time we don't use a lot of hot water, and our 117 litre cylinder is more than big enough. Sometimes we...