The phase diagram of a poly(ethylene oxide)/poly(ether sulphone) blend is constructed using modulated temperature DSC and optical microscopy. It includes the glass transition (T-g), melting point (T-m) and cloud point temperature (T-g), which define the regions of interest in this work: demixing above T-cl, followed by remixing in the miscible melt region between T-cl and T-m or T-g. The width of T-g has to be taken into account to understand partial vitrification effects during phase separation at high temperatures. Dynamic rheometry provides complementary information about partial vitrification and devitrification. Excess contributions due to demixing and remixing on the time-scale of the modulation appear in the heat capacity in both non-isothermal and quasi-isothermal conditions. This apparent heat capacity signal is used to study the effects of composition of the blend and molecular weight of the constituents on the demixing and remixing kinetics and on the interrelation between both. Partial vitrification during demixing is important in this respect. Step-wise quasi-isothermal measurements show a time-independent excess heat capacity in between T-cl and the interference of vitrification.