Patent ID: 7996182

Claim:
For use with a water heater in which heated water is stored for on-demand delivery therefrom, the water heater having a predetermined heated water setpoint temperature T max and a predetermined minimum water temperature T min , monitor/diagnostic apparatus comprising: a monitoring portion operable to detect the temperature T meas of the stored water and responsively generate an output signal indicative of its magnitude; and a diagnostic portion operable to: initially determine a first total recovery time of the water heater from T meas =T min to T meas =T max with the water heater in an initial condition thereof, subsequently determine a second total recovery time of the water heater from T meas =T min to T meas =T max , compare the second total recovery time to the first total recovery time, and generate a diagnostic signal indicating to a user the need to service the water heater, due to an unacceptable loss in efficiency, if the second total recovery time is greater than the first total recovery time by a predetermined factor.