A flow sensor circuit for a fluid flowpath comprising: a processing unit, a self-heated thermistor, and a constant voltage or constant current source; wherein said self-heated thermistor is situated in the fluid flowpath; said flow sensor circuit is configured to: apply a high current to said self-heated thermistor during a first time period; obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a second time period; calculate the average (T2av) and standard deviation (T2sd) of said measurements obtained during T2 using said processing unit; apply a low current to said self-heated thermistor during a third time period; obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a fourth time period; calculate the average (T4av) and standard deviation (T4sd) of said measurements obtained during T4 with said processing unit; and ascertain the state of said flowpath using said T2sd and said T4sd with said processing unit, wherein the state of said flowpath indicates whether the fluid in the fluid flowpath is flowing normally, contains bubbles or is clogged, or contains air or is stopped. a processing unit, a self-heated thermistor, and a constant voltage or constant current source; wherein said self-heated thermistor is situated in the fluid flowpath; said flow sensor circuit is configured to: apply a high current to said self-heated thermistor during a first time period; obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a second time period; calculate the average (T2av) and standard deviation (T2sd) of said measurements obtained during T2 using said processing unit; apply a low current to said self-heated thermistor during a third time period; obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a fourth time period; calculate the average (T4av) and standard deviation (T4sd) of said measurements obtained during T4 with said processing unit; and ascertain the state of said flowpath using said T2sd and said T4sd with said processing unit, wherein the state of said flowpath indicates whether the fluid in the fluid flowpath is flowing normally, contains bubbles or is clogged, or contains air or is stopped. apply a high current to said self-heated thermistor during a first time period; obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a second time period; calculate the average (T2av) and standard deviation (T2sd) of said measurements obtained during T2 using said processing unit; apply a low current to said self-heated thermistor during a third time period; obtain multiple measurements of the temperature of said self-heated thermistor with said processing unit while said high current is applied to said self-heated thermistor during a fourth time period; calculate the average (T4av) and standard deviation (T4sd) of said measurements obtained during T4 with said processing unit; and ascertain the state of said flowpath using said T2sd and said T4sd with said processing unit, wherein the state of said flowpath indicates whether the fluid in the fluid flowpath is flowing normally, contains bubbles or is clogged, or contains air or is stopped.