Yes, back to the OP!
The advent of condensing boiler has led to the adoption of some new descriptions although they are somewhat arbitrary!
There are two basic boilers from the point of view of their application.
Combi boilers and heat only.
Boilers are either "standard" ( efficiency) or condensing!
All combi boiler are complete units with a pump, pressure gauge and expansion vessel ( apart from those very few which are suited for an Open Vented system.)
The cheapest is a basic heat only boiler with no pump, pressure gauge or expansion vessel. They are mostly suitable for sealed or open vented use.
Then there is a more expensive heat only boiler with most of the bits inside, pump, pressure gauge and expansion vessel, these are called "system boilers",
Does this answer your query?
Tony Glazier