Abstract: The invention relates to boilers using solid fuels in granular form.It comprises: (a) automatic feeding of the firebox with fuel by a reciprocating piston system forming a fire barrier in the rest position and actuated by a low power linear movement motor, and (b) combustion quickened by the supply of blown air and stirred by a system for discharging ashes and combustion residues out of the burner by the action of fingers integral with the piston.This type of boiler is suited for central heating as well as any other domestic or industrial hot water production.