FLUID HEATER WITH FREEZE PROTECTION

A heat source is disposed in the thermally conductive mass housing for imparting heat to the mass. Fluid in a flow path through the mass absorbs heat from the mass. A fluid expansion member is mounted over open ends of the fluid flow path. The fluid expansion member, in one aspect, is formed of a compressible material to compress under the forces of fluid phase change to a solid state and expands back to a nominal shape when the fluid undergoes a reverse phase change to a liquid state. In another aspect, the fluid expansion member is a solid seal member overlaying the open ends of the fluid flow channels. The seal resists expansion under normal fluid operating pressures, but expands into an open interior chamber in a closure fixed to the mass to accommodate a phase change expansion of the fluid.