How does TPI Control work?

A thermostat operates using a fixed number of firing periods per hour (normally selected to suit the appliance and system). This can often mean a thermostat can fire the boiler even when the set temperature is reached.
A TPI room thermostat will have 100% demand when the system first calls for heat. When the room temperature approaches the set point, it then calculates how many minutes are required within each firing period to satisfy the set temperature. The TPI thermostat will then reduce the firing time in that cycle period in proportion with the demand. This means that as the room temperature approaches set point, the boiler is fired progressively less.