Be it electric or gas there are two basic ways to control a boiler output, one is the analogue control the other is digital the latter using a mark/space ratio, however with electric that mark/space can be a rather short time, possibly seconds or even shorter, however with gas, the time is a lot longer, so with gas one has to be careful not to use a unit which is too big. There is it seems a minimum flame height. So where possible the gas boiler should be controlled by the return water temperature and only when the flame is at a minimum setting should the electric control take over.
I was taught the wall thermostat is there to turn off the heating when no longer required, it is not there to control the room temperature. To control room temperature with a wet system you need to measure the temperature very close to the radiator and measure both air and water temperature the latter used to compensate for the air temperature being measured close to the source.
As an industrial electrician I have been required to heat all sorts, wax, steel, and rooms. Using not only gas and electric but also oil and solid fuel, one of my jobs was to write the software to control the heaters and reduce the hysteresis to a minimum. Using solid state contactors easy enough with electric heaters the time between each pulse can be short, but using heat pumps one has to allow the pressure to equalise before a restart, so using inverters and altering motor speed instead of simple on/off works better, like gas there is a limit minimum and maximum speed.
I have tried many times to design the system. And straight from Uni out came the slide rule to work it all out. However quickly I realised too many variables, it actually works better looking at the task, and saying this is similar to the job I did at xxxx but half or twice the size so it will likely need a heating unit of xKW, one considers the last one proved too big, or too small.
In the main we have to use units of 3kW, 6kW, 12kW etc, working out it needs 4.25kW is rather pointless if you can't buy a 4.25kW unit, one uses experience, you look at the room, and you say to ones self 3kW will be too small think it with need a 6kW, yes you could work it all out, but why?
If you buy a car to get to work, you don't work out what size of engine is required to get you to work in 1 hour, you use experience, and you say I'll have that one, you have considered all the pros and cons but you have not worked out the engine size, even with wagons you clearly have to satisfy the so many BHP per ton rules, but you look at reliability more than engine size.
Yawn!!...........Really?? Amazing!!