A starter system for start up of a combined heat and power unit comprising a generator which is connectable to the grid. The starter system comprises a variable frequency drive, VFD, operable to receive power from the grid. The VFD reduces the frequency of the power, and provides the reduced-frequency power to the generator to start the generator. The starter system further comprises a bypass relay configured to bypass the VFD. The bypass relay allows direct connection between the grid and the generator after the generator has started. The variable frequency drive is configured to operate temporarily during start up of the combined heat and power unit.