Condensing boilers generally have a modulation of 1:8 or even 1:10.  The minimum power can make 24KW (modulation for 24KW boiler is 1:10). Non-condensing boiler, restricted by the burner, modulation of which can make 1:3, or even 1:3.5, though very hard.

When it approximates thermal equilibrium,the heat load is small. Condensing boilers can work at small load, and the temperature will not rise 2~3℃ higher than the set value. The boiler doesn’t stop but runs at low fire. Generally the heat output power can be increased (almost all condensing wall-hung boilers can be modulated)