Thought I would ask my own combi question as currently trying to choose for my flat.

Large 1 bed flat with 2x 600×1200 double rads, 1x 600×700 single and a towel rad.

I want a boiler that can run a thermostatic mixer with a nice big head, fixed off some chrome piping and not have one of those rubbish little heads off a flexi hose which look all scummy in no time.

I know a 30kW boiler is overkill for the CH but will the DH flow on anything less than 30kW be okay for a decent shower?

Has to be either WB or Valliant.

Also any controller recommendations? Would prefer to stick to the manufacturer ones.

Flat will be rented out when I finish it but possibly only for a year. Currently have a 10.5kW electric shower in but want to get rid of it.

Honeywell controls are my preferred choice.

Water flow will only be as good as that at stopcock.

fixed head shower may need more water than can be supplied by a water main. Some of the fixed heads need huge flows and pressures, depending on size.

But a big combi will produce a decent flow, better would be an unvented cylinder with heat only boiler, that way can match boiler to heating load.

nail on head from bear.
i fitted a 42 kw to a shower importers house he had 3 fixed head 1 main bathroom 2 ensuite and a downstairs loo.. i had my fingers crossed that a combi would cope but that bad boy ran a shower and filled the bath in under 5 mins, at the same time
honeywell controls reliable solid good but not cheap wb controls as good but expensive and not always reliable esp wireless.
i usually fit a salus programmable stat which gives the user flexible positioning and relative reliability ( 5 yrs and not a bust one)and at 50 folding there throw away..

Water pressure is so high the shower head on the end of the bath can hover at shoulder height when the cold is turned on high! (as long as you steady it with your hand)

I hadn’t really considered a tank type system – having just ripped one out. I mains pressure one would work well I guess but my old tank put me off being poorly insulated (cupboard was too small for it so it was right up against the back wall) so I didn’t use it and just had a kettle for doing the dishes and electric shower.