Analogue thermostat is one which gradually increases or decreases the heat output to area measured to maintain heat at required level, a digital thermostat uses a mark/space ratio to increases or decreases the heat output to area measured to maintain heat at required level.
There are cases where analogue is approaching digital, as with fan assisted radiators, where there maybe just two speeds and off, and the thermostat is not truly analogue, but really two stage digital so fan switches on at say 20.5°C then switches to high speed at 20°C, even when a 4 speed fan is used, so 20.5°C, 20.3°C, 20.1°C and 19.9°C one could argue either way as to if analogue or digital, I would personally call it digital, however where there are 255 stages even if not truly analogue most consider it to be analogue.
Same as a cooker control, the simmer-stat is digital, as the time between on/off is rather large, however with induction hobs although it may actually still switch on/off or chop the wave form, it works like an analogue control, so even if not strictly speaking analogue I would still call it analogue.
So for the central heating in this house there are multi analogue controls, and also two digital controls.
So the TRV gradually open and close (analogue) as the close the water pressure increases which in turn causes the by-pass valve to slowly open (analogue) this allows the return water to get hotter and hotter, and the boiler gradually compensates by reducing flame height (analogue) however once the flame height is at a minimum then the boiler starts to cycle (digital) and as the whole house warms up in the end the hall thermostat switches off (digital) stopping the boiler cycling. As the hall cools the thermostat will turn on again, but this only happens when the house as a whole is using less heat than the minimum output of the boiler.
The system is not correct, I should have a wave thermostat in the hall which will tell the boiler to reduce the output, in real terms this equates to the temperature of the circulating water, since before the boiler turns off the water would be cool anyway, then less heat goes out through the flue every time the boiler starts to cycle, however the daft installers ripped out the hard wired thermostat and replaced it with a wireless one, and wave needs a wired connection not wireless, so the cost to reinstate the hard wired thermostat means I am forced to use a digital thermostat to finally turn off the system as warm weather returns, or do it manually.
However since the is a limit to how much a boiler can be modulated, Autumn and Spring there has to be some digital control, however in winter it should be all analogue control. Analogue control means little or no hysteresis in the temperature, digital control means a high hysteresis, so whenever possible we should use analogue control.
