"What is a Condensing boiler?
Good question, if it boils the water then the condensing would be done in the radiators, not the boiler, and if it does not boil the water then clearly it's not a boiler.
However the latent heat, or condensing of the moisture is not referring to the circulating water or steam, but the water produced as we burn the fuel, I have seen two designs for a wood burner that condenses the water out of the flue gas, but in the main only gas or oil condense the moisture out of the flue gas, and to do this with a circulating water system the return water needs to be cool enough.
The "Rocket" solid fuel heater does not use water or air to transmit the heat into the room, it heats up stones, so there are exceptions, but in the main the problem is getting the return water cool enough.
So when the water heater is controlled by the eBUS then the return water can be kept very cool, but where the water temperature is used, then the hotter the return water the lower the flame height, so the water is hottest just before the boiler switches off, although one could allow the pump to run for a time after the boiler has switched off, in theory that will not work, and reason hot water has returned is the thermostatic radiator valves have closed causing the by-pass valve to open so the water has no where to circulate other than within the water heater.
So using the eBUS less heat is lost every time the boiler turns off. But next question is who actually uses the eBUS to control the boiler, clearly it will be used when the boiler is tested, but building management systems are expensive, so even if theory shows eTRV which talks to a central thermostat which in turn uses OpenTherm to tell the boiler flame height required, in practice very few systems actually use it.
Same applies to radiator type, modern idea is never turn either the radiator or boiler off, we just alter the output. (Modulate) And to save energy we only heat the room when required, so the room can both heat up quick and cool down quick we want to keep the quantity of circulating water down to a minimum. Before modulating systems the reverse was true, we wanted the water in the radiator to act as a heat reservoir, smoothing out the mark/space action of the boiler, but today best option is to control the fan speed in fan assisted radiators which because they are fan assisted can heat the room far faster.
However again theory and practice are very different. The radiator will send out information as to room temperature and fan speed, but the unit to collect this and adjust boiler output is super expensive, plus to use a fan to circulate the air, there is noise from the fan, and if there are any poorly insulated parts in the room, then circulating the air will increase losses.
Any semi-skilled guy can follow a plan putting pipe A into hole A and wire A onto terminal A and install a system using something like EvoHome. The software does all the cleaver stuff. However EvoHome and the like is not cheap, so the skilled man can do nearly the same using far cheaper equipment, now that takes skill. But he can only do it if he knows what is wanted. I know IT guys would have signs on their desks. "We did exactly what was asked, but it was not what was wanted." That is also true with central heating.
So you want the kitchen to heat up ready for your return, followed by the living room, and at 10 pm the living room is allowed to cool and bedrooms heated etc etc. However you live 25 miles from work, so the geofencing is set to 20 miles, that takes 30 minutes so heating has been off all day and comes on as you travel home. However the eTRV has a minimum setting of 16°C and set to 20°C within 15 minutes it has hit 18°C, however in order no to over shoot the system now slows up, so it is another hour and a half before it hits 20°C. By 10 pm the room is warm, and the eTRV switches to 16°C but again so it will not over shoot it looses 2°C quickly but then slows down, and only on the coldest of nights will it ever cool to 16°C. Added to that, loads of insulation inside home to outside, but very little between rooms, so bedroom may be set to 18°C but in the main it still sits at 20°C.
So all this cleaver control is completely wasted as the house simply will not warm up or cool down that quickly. So central heating is 60% house design and 40% central heating design, and if your house is not designed to be able to use all the smart controls, then they are simply a waste of money.