Best central heating means you work from radiator back, so you want a radiator that will respond quickly to demand so it can work well with geofencing, so the matrix needs to be small so it warms up quickly, so looking at fan assisted radiators like the Myson iVector, for this to work efficiently it needs a building management system, and for the building management system to work A1 likely we are looking at a heat store so a small boiler can provide the instant heat required as you approach home. So since using a heat store the boiler will run at a fixed rate on once heat store hits lower limit and off when it hits upper limit so boiler can be rather simple.
However in the real world we use a compromise, and so we don't want best boiler, but some thing near enough. Still looking at control, once not using a heat store, you want boiler to modulate, and if your going to control the boiler modulation with electric system then you need the system your using to integrate with the boiler, so with an open plan house using a single thermostat worcester bosch with Wave may work A1, but if you have rooms with doors then you need a system that combines the needs of the TRV heads to tell the boiler what output is required, so if the boiler is not OpenTherm it's a non starter.
If using the boiler to fill a bath direct then looking at around 28 kW minimum, but a shower direct 18 kW is ample, clearly also depends on losses from the house, but the lower the boiler will modulate to, the less the boiler with cycle so the more constant the temperature and the less heat lost to outside, so if you could get a 4 kW to 18 kW boiler for my house that would be A1, however not seen a boiler that small.
Now to install a boiler you need to be registered as gas safe, and every registered guy will have his favourite supplier and will work with a limited range of boilers, and if he is using a product he knows well he can fault find fast and likely has a stock of parts, so yes ask for an OpenTherm boiler, so it can link to the very best control system, and yes you can even work out what size you require, but if your local supplier does not normally fit worcester bosch then to ask him to fit that make is asking for trouble.
So in the real world you find an installer and use one of the range he normally fits, even if there is a better boiler on the market, so in real terms you may find you only have a chose between worcester bosch and vaillant because that's all your local installer uses, yes there may be better, but any mechanical item will at some point break down, so you want some one that when it does break down they can fix it fast, that means something they keep parts for in stock.
I have romanced many times about the best system, and I know what I have is not the best, my worcester bosch does not have OpenTherm, in fact it will not work with Wave, and the thermostat cycles as it approaches the set temperature and is completely the wrong type, but it has not broken down and if it does I can get a fixed price repair from worcester bosch after one phone call, so although far from best, it is good enough.
