Mr Tiampati and five other officials, who were suspended on June 20, were to know their fate after the lapse of a three-month leave.
The board said the suspension would allow investigations on their conduct.
Other members who were sent on leave include company secretary John Omanga, managing director Alfred Njagi, finance and strategy director Benson Ngari and David Mbugua, general manager ICT.
The board said forensic audit of the operational and financial system will be undertaken in due course and that procurement contracts will be reviewed to ascertain value for money and determine if the services and goods were obtained within the market benchmarks.
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