New boiler - how ensure efficient operation?

[p7777m]

I'm having a new boiler installed to replace my exceedingly reliable Potterton Netaheat 16/22.
I've been offered this:
Glow Worm Ultracom 18HXI or Vaillant Ecotec Plus 418 (+£360)
Grundfos 15-60 high head pump
S plan, autobypass valve
Magnaclean
Power flush
Honeywell cylinder stat, (single) room stat, programmer.
Fully vented.
(HW cylinder is indirect, fully vented)

How do I ensure that my boiler runs as efficiently as possible & spends as much of its time as possible in condensing mode...
(a) - at install time, by influencing the choice of components and how/where theyr'e installed - ?
(b) - and after install, when the system is in use?
I believe I should be asking for a Grundfos Alpha instead, in order to give the boiler a better chance of minimising non-condensing operation. Is that right?
Have the releability issues of earlier Alphas really been addressed?
Any thoughts or recommendations on this combination and how it could be improved?
Is there anything else I should consider?
I've been told the Glow Worm Ultracom 18HXI is pretty much identical to the Vaillant except for the case. Is this correct? What does "pretty much" mean - are there any internal differences you're aware of?

 

[Hufty]

Vaillant/GW are part of the same group - lots of common parts in them. Main thing to ensure at this stage is that you get the weather compensated control for the boiler you get (VRC430/Climapro2) instead of whatever you're thinking of. It's the controls that matter. Then you can sit back and let the software keep it all condensing as much as possible whilst you do something else. (Others will post to disagree about the efficiency of weather compensation - ignore them.)

Would also make sure you have TRVs on every radiator (except possibly the one near the VRC430/Climapro) and that they work (rad shouldn't get hot with TRV on position 1). Oh and when it's up and running don't have them all on maximum.

Would also look at your cylinder lagging etc, and rather than the cylinder stat would consider using the sensor which comes with the VR65 you would need for the Vaillant to control the cylinder. (This not approved to the letter of the law, but efficient, and the building regs will catch up in a few years.)

As someone who fits Vaillant boilers, I was surprised at some of the design details and the wiring route of the open vent boilers - would go for a 618 myself if possible then the pump decision is made for you and you can lose a header tank.

Auto bypasses with a condensing boiler, good or bad? Discuss.
Varispeed pumps good or bad? Discuss.
Varispeed pump with an auto bypass? Oy vey!