An apparatus is provided for a heating appliance that includes a manually-opened pilot valve that is held in an open position when a sufficient voltage is applied to a valve operator, and a thermocouple that converts heat from a pilot flame into a voltage that is applied to the valve operator. The apparatus includes a voltage measuring circuit that provides an output indicative of a magnitude of the voltage generated by the thermocouple, and a light emitting device. A controller is coupled to the voltage measuring circuit and the light emitting device. The controller is configured to establish, based on the output indicative of the magnitude of the voltage generated by the thermocouple, a switch sequence for switching the light emitting device on and off in a flashing manner, to provide an indication of when the magnitude of the voltage is sufficient to cause the valve operator to hold the gas valve open.