The Plumbing Group have produced a number of Cylinder Plumbing & Wiring Diagrams. This is to help engineers with installation and fault finding on vented and unvented hot water systems. The red drop down tabs are electrical related. The blue drop down tabs on the other hand are plumbing related.
Cylinder Plumbing & Wiring Diagrams Unvented Systems
These diagrams are specifically for unvented systems.