This paper presents a simulation study to explore the flexibility of a pool of residential combined heat and power plants (cogeneration systems) coupled with thermal storages. Flexibility is identified by sending daily trigger signals (ON and OFF) of various signal lengths to a pool of 60 micro cogeneration systems over the course of one year. A randomization approach is used in order to reflect realistic system sizing based on commercially available components. Each system operates individually based on its thermal demand. The response of the pool to the external signals is evaluated. Flexibility is characterized by flexible power, flexible energy and pool regeneration time. Results show that both signal types can potentially activate a significant amount of flexible power and energy. The flexibility is highly dependent on the ambient temperature and the signal duration.