A valve arrangement, especially for controlling flow of hot water through a heating device of a motor vehicle, mainly comprises a closed housing provided with an inlet chamber and an outlet chamber communicating with each other through an opening forming a valve seat, and a valve member movable relative to the valve seat for opening and closing the opening. The arrangement includes further a flexible membrane which is clamped at its outer periphery to the housing and which forms a control chamber at the side of the inlet chamber facing away from the valve seat. The valve member is operated by an electromagnet which acts also on an auxiliary valve member in the control chamber to create during movement of the valve member toward the valve seat a higher pressure in the control chamber than in the outlet chamber and during movement of the valve member away from the valve seat a lower pressure in the control chamber than in the inlet chamber.