Interesting. I got a 627 system boiler. Vsmart and a vaillant unistor. I have 14 rads a big 5 bed house. 1960s home. Large windows. Cavity with retro fitted insulation. I am using 26000kwh a year on gas. I do use have a gas job but that’s it. I still expect a bit better.
9x rads, Econofit 418, with outdoor temperature sensor - rest of the system is 40 years old, in a semi, gas hob, double gas oven. DG, CWI and I uses 10130Kw over the past year.
As I mentioned earlier, I am experimenting with gas consumption for this winter, making more use of the previously unused living room gas fire.
Vsmart however always get tempreture set very well with little or no spikes.
Same here and I constantly record my indoor/outdoor temperatures. It has never over shot - it just throttles down perfectly, then just maintains the temperature silently.