A traditional system is now the combi as they are approx 60% of the market in sales and have been for around 5 years.
Many combis of differing makers, share the same components, which are available readily off-the-shelf, even the pumps are standard available from B&Q. HRPC, who are in all Plumb Centers, stock most generic boiler parts.
You know what I'm talking about Doctor Drivel or should I call you Water Systems, Richard Hanson Granville or whoever else you post as.