greenstar cdi and premier plus unvented

[daz1963]

hi guys been lurking for a while and now need to ask for some advice. don,t do a lot of s plan and y plan stuff so not to sure about a few things. i,ve got a greenstar 40 cdi conventional and a premier plus unvented mains pressure water heater. do these run off there own 13 amp fcu or does the premier run off its own 13 amp fcu and the greenstar connect in to the wiring center. so ineffect there is just one fcu for the two of them.also on the greenstar theres a connection to go to the external pump. is this lz to connection 14 of the wiring center and nz back to neutral. hope this makes sense to someone and would appreciate a bit of help. if anything is unclear i will try and explain a bit better. many thanks in advance...
daz...