The necessity for a highly accurate and reliable geoid model to enable a prompt determination of normal height with the use of GNSS coordinate determination is needed due to the high precision requirements in geodesy, building and high precision road construction development. Additionally, the Latvian height system is in the process of transition from BAS-77 (Baltic Height System) to EVRS2007 system. The accuracy of the geoid model must approach to the precision of about ~1cm looking forward to the Baltic Rail and other big projects. The use of all the available and verified data sources are planned to use including the enlarged set of GNSS/levelling data, gravimetric measurement data and, additionally, the vertical deflection measurements over the territory of Latvia. The work is going ahead stepwise. Just the issue of GNSS reference network stability is discussed. In order to achieve the ~1 cm precision geoid it is required to have a homogeneous high precision GNSS network as a bases for ellipsoidal height determination for GNSS/levelling points. Both the LatPos and EUPOS® – Riga network has been examined in this article.