I am looking to move house, and I am well aware of heating costs, so read up on how modern central heating works, ideal system using fan assisted radiators is so expensive to install it is very rarely used, so in the main we use TRV to control heat to each room. There are two ways to use a modulating boiler, one uses the return water temperature, the other has a modulating thermostat fitted, the latter more expensive to install but means the boiler is cooler when switched off so less energy lost to outside. However in both cases it works by the TVR and/or boiler slowly opening or closing and flame height lifting or lowering to match, i.e. an analogue control. However motorised valves have set positions, closed, centre, open, there is not analogue control it is open, closed or half way, I note with interest central heating systems with modulating boilers and TRV plus motorised valves creating zones or selecting domestic hot water and/or central heating, and I just can't work out how the digital zone valve i.e. on/off is matched to an analogue boiler? Is there a way? or did the installer not have a clue what they were doing?