Abstract: A system for monitoring the operation of a heating apparatus having a combustion chamber with associated air and fuel supplies and an exhaust path includes sensors for monitoring temperatures at the combustion chamber. A microprocessor and a display receives signals from these sensors and has a keypad to permit calculation and display of parameters indicative of proper operation of the heating system including fuel usage per unit time. Limit values can be stored in the processor memory to trigger alarms when temperatures or fuel usage exceed the set limits. Various measured and calculated values can be displayed.