Method for controlling a heating appliance and heating appliance

Method for operating the heating system in a motor vehicle whereby the outputs of sensors upstream and downstream of a heat exchanger region are used to control the heat output of a heat source supplying heat to the heat exchanger region. An Independent claim is made for a heating system comprising a heat source, a heat exchanger, a fluid inlet and a fluid outlet, whereby in the heat exchanger region between the inlet and outlet, heat is transferred to the fluid from the heat source. A sensor arrangement is provided to measure fluid temperature upstream and downstream of the heat exchanger.