A high temperature fluid generator is configured to heat a fluid (e.g. water; thermal oil or the like) to a high temperature (e.g. greater than 250 degrees Fahrenheit or 120 degrees Celsius) using a fuel-burning furnace. The generator generally comprises a furnace module, wherein fuel is burned, and a convection module where the combustion gases are put in contact with a series of fluid-bearing convection tubes. The furnace module comprises a series of fluidly interconnected headers, some of which are also fluidly connected to the convection tubes in the convection modules. The various headers contribute to the overall structure of the generator. The convection tubes are arranged into at least two bundles which are movably mounted in the convection module of the generator such to be movable in and out of the convection module for inspection, cleaning, maintenance and/or repair.