Assembly for controlling the feed of fuel to a heating apparatus having an air passage (1) with a sluice located therein, formed by or comprising a valve (15, 45, 75) which is movable for varying the air passage and fuel-metering means (16, 17) communicating with a portion of the air passage in the area or downstream of the sluice for metering the fuel supply depending on pressure prevailing in the area or downstream of the sluice, a burner (5), a discharge channel (6), and a fan (3) for driving an air flow (7, 8, 11, 68) through the air supply channel (1). As the valve (15, 45, 75) is arranged for limiting the air passage (1) in response to the fall of a pressure drop over that valve (15, 45, 75) below a specific value, heat loss caused by air displacements when the fan (3) stands still is prevented without using a separate valve, and an enlargement of the work area of the heating apparatus is obtained.