Not fitted a system before. Customer wants a worcester as above. Had a look at the manual and there are 2 different wiring schemes. One for a system boiler with and one without a diverter valve. Whats the reason for this. Also the one without out has two stats on the cylinder , a cyclinder stat and a temperature cylinder stat - can anyone enlighten me on this? The wiring seems pretty straightforward but I'd like to understand the pluses and cons of these 2 variations of this system boiler.