The Steam Generating Heavy Water Reactor (SGHWR) was of significant interest in the UK in the late 1960s and early 1970s but failed to be developed into a commercial programme. This paper reassesses the reactor physics of the SGHWR with modern day modelling tools: neutronics and thermal hydraulics are coupled using Serpent and THERMO. Such a coupling is required since the boiling coolant along the SGHWR pressure tube height will have a significant influence on the neutronics of the system. Results show that the coolant void coefficient is negative at nominal conditions. This is achieved by the important contribution of the coolant towards moderation. Plutonium build-up throughout burnup also has a beneficial effect on the void coefficient. Quasi-static analyses of mass flow changes, pressure changes, and overpower events are examined. Most importantly, the power coefficient is negative. Superheated steam coolant conditions are also simulated for a SGHWR pressure tube. Although the steam temperature coefficient is slightly positive, the power coefficient is also negative.