Abstract: There is provided a control unit for controlling the operation of a fuel valve. The control unit includes a first relay and a second relay. The first relay and the second relay are connectable in series and oppositely actuable. The first relay is actuable in response to a first control signal. The second relay is actuable in response to a second control signal which is inverted with respect to the first control signal. Thus, the relays are differentially operated. Further, there is disclosed a scanner control unit which reduces the noise of a voltage signal whose magnitude is representative of the intensity of a monitored flame in a boiler. The flame scanner control unit uses a comparator to reduce the noise in the voltage signal. The voltage signal is provided at one input of the comparator and a reference signal is provided at the other input of the comparator. The reference signal is representative of the intensity of noise in the boiler when the monitored flame is out.