Version 6 of ESATAN/FHTS will soon be out in the field and the users will benefit from the large number of improvements made during FHTS Upgrade 1. Behind the scenes the upgrade programme continues; this paper discusses the major areas of technical development. Simulation of two-phase cooling loops is becoming increasingly more important in the space industry. To fulfill this requirement two new two-phase solution modules have been developed: one a pseudo-transient for simulations where the hydraulic response is negligible; the second performing true transient analysis using a fully implicit scheme, giving a stable solution for large time steps. Results from these are presented and discussed in the paper.A capillary pump model is currently under development with the aim of enabling capillary action to be simulated using performance curves. This approach is being adopted to avoid degradation of solution speed, yet provide sufficient accuracy and flexibility. To enhance the modelling capability of FHTS a fixed temperature-only status has been implemented to complete the set of fluid boundary conditions.