A flow-through heating apparatus which senses temperature in a fluid conducting means through which the fluid flows, comprising:
- a first heating means located within said fluid conducting means;
- a first temperature sensing means associated with said first heating means for sensing the temperature of the fluid within said fluid conducting means;
- a second temperature sensing means, located within said fluid conducting means downstream from said first heating means and said first temperature sensing means;
- a control means including a set point temperature means for varying the temperature sensed by said first temperature sensing means when there is no fluid flow while the temperature sensed by said second temperature sensing means remains relatively constant after drifting toward an ambient temperature;
- and
- said control means further including a temperature comparison means for detecting fluid flow when the temperature sensed by said first temperature sensing means converges with the temperature sensed by said second temperature sensing means;
- a second heating means located within said fluid conducting means downstream from said first temperature sensing means and associated with said second temperature sensing means;
- said control means further including means for selecting an operating set point temperature to which the fluid is to be heated when there is flow through said fluid conducting means;
- said control means further including means for transitioning the temperature of the fluid by targeting a transitional set point temperature between a standby set point and said operating set point;
- said control mean further including means for incrementing said transitioning means which is activated when said operating set point is greater than said transitional set point and the temperature of the fluid sensed by said first temperature sensing means is not greater than the temperature of the fluid sensed by said second temperature sensing means;
- said control means further including means for decrementing said transitioning means which is activated when said transitional set point is greater than said standby set point and the temperature of the fluid sensed by said first temperature sensing means is greater than he temperature of the fluid sensed by said second temperature sensing means;
- said control means further including means for incrementing the demand on said first heating means activated when said transitional set point is greater than the temperature of the fluid sensed by said second temperature sensing means and the demand on said first heating means is not at a maximum demand;
- said control means further including means for decrementing the demand on said first heating means activated when said transitional set point is not greater than the temperature of the fluid sensed by said second temperature sensing means and the demand on said second heating means is substantially equal to zero;
- said control means further including means for incrementing the demand on said second heating means activated when said transitional set point is greater than the temperature of the fluid sensed by said second temperature sensing means, said first heating means is at the maximum demand and the demand on said second heating means is not at the maximum demand;
- and
- said control means further including means for decrementing the demand on said second heating means activated when said transitional set point is not greater than the temperature of the fluid sensed by said second temperature sensing means and the demand on said second heating means is not substantially equal to zero.