partial wall 82 the plurality of equivalent equispaced elongate slots 66 is defined between adjacent walls 64 or a wall 64 and adjacent partial wall 82 the slots 66 serve as ports or outlets for fuel gas air premixture for subsequent ignition as will be described below each slot 66 has an inlet portion 84 which is defined between adjacent tapered upper wall portions 70 and converges to an end 84a which leads to a substantially constant dimension straight portion 86 between adjacent parallel walls 76 78 an outlet portion 88 diverges from the end 86a of the substantially constant dimension portion 86 remote from the inlet portion 84 each lower wall portion 72 of the walls 64 has at its free lower end a central recess 87 which extends completely through the thickness of the portion over a part of its length and is in alignment with the equivalent recesses 87 in the other wall portions 72 to provide a cross lighting path 90 across the burner flamestrip 50 in the ready for use condition the assembly of components described above is mounted on a combustion chamber 92 as shown in chain dotted lines in fig1 by means of an apertured flange 94 which extends outwardly from and around the walls.