I have seen control systems sold as C, W, Y, or S plan, what the difference?
Are there any other common setups
(These are water based CH systems, so are unlikely to be used in the USA)
The type of plan refers ultimately to the arrangement of the pipes and thus the type and number of valves you have in your system.
This page has explanations of all types (Y, S, W and G (not C)). Y Plan is based on a single three way valve that either allows the hot water from the boiler to the heating circuit, hot water circuit or both.
The W plan is an older control system.
The G plan is for gravity assisted systems. I couldn't find a "C" plan though.
I've also found this page which has diagrams of the Y-Plan and S-Plan controller circuits. They're quite technical so I'm reluctant to summarise here.