The improved combustible gas sensor of the invention includes a housing defining an interior containing a reference bead and a measurement bead which are fully exposed by the removal of a shroud. The beads are connected in series and the reference bead is connected in parallel with a resistor to define one side of a Wheatstone bridge. A liner consisting of a disk (46) defining an inner face (48) and an outer face (50) overlies the reference and measurement beads. The inner face of the disk is provided with a slot opening (58) at the inner face which is dimensioned to receive the reference and measurement beads. The slot provides a confined space for fluid communication between the exposed beads. A channel extends from openings in the disk and communicates with the slot. The disk is recessed and has a porous closure defining a plenum in which the sample gas is received.
