The Boiler Control Cylinder Stat is identified by having 3 connections on the right hand side (seen in above image).

The Immersion Heater Control Stat is identified by having 2 connections on the right hand side. See below link for this product.

https://kepartsshop.myshopify.com/products/thermostat-for-immersion-heater-control?_pos=2&_sid=2fed5126c&_ss=r