When you initially turn on the hot tap, you draw the water that has been stood in the pipework between the PulsaCoil and the tap itself. It is not until this water is drawn off that you then receive the hot water that is generated by the PulsaCoil. This is unavoidable and would be experienced with ANY boiler.
You may experience a fluctuation in temperature of the water for a further 20-30 seconds. This is just the unit adjusting the output temperature to the taps as it passes the sensor on the unit.