This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.A simple 1-D model is presented to study the effects of the wall heat flux, location of the nucleation site, channel dimensions and fluid properties on the pressure fluctuations caused by confined bubble growth in rectangular microchannels, for zero upstream compressibility. A simple isothermal compressibility model is then used to study the effects of the initial volume of non-condensable gas trapped in the upstream plenum, initial inlet velocity and nucleation site location on local pressure fluctuations and transient flow reversal. Both acceleration pressure drop and viscous pressure drop are considered.This work was supported by the Engineering and Physical Sciences Research Council, Grant EP/D500095/1.