Abstract: Test apparatus is disclosed for testing a gas-fired forced air heating system having a plurality of control elements. A monitoring device includes an indicator light adjacent to the thermostat for indicating a malfunction in the heating system, the monitoring device including condition-responsive switches for energizing the indicator in response to the absence of a stream of heated air when called for by the thermostat or in response to a malfunction in the thermostat. An analyzer comprises a plurality of indicator lights connectable through a selector switch to the power source and the heating system, the switch having an "OFF" condition for disconnecting the indicator lights, a "TEST" condition for checking the condition of the indicator lights and an "ON" condition for connecting the indicator lights respectively in parallel with corresponding heating system control elements to test the conditions thereof. Two embodiments of the analyzer are disclosed for use with different types of heating systems.