Premix gas burner, comprising - a main body; wherein the main body comprises a cylindrical shape; - a porous wall; - a distribution chamber delimited by the main body and by the porous wall, - an entrance in the main body for introducing a premix of combustible gas and air into the distribution chamber; wherein the porous wall comprises a first porous wall segment and a second porous wall segment; wherein the first porous wall segment and the second porous wall segment both comprise pores for the premix gas to flow from the distribution chamber through the pores for combustion of the premix gas outside the distribution chamber; wherein the first porous wall segment comprises or consists out of a shaped segment, wherein the shaped segment is directed to the inside of the distribution chamber, such that when the burner is in use premix gas flows from the distribution chamber through the pores of shaped segment to the inside of the shaped segment; wherein the shaped segment widens in the direction away from the entrance in the main body wherein the second porous wall segment comprises an annular porous wall segment; wherein the annular porous wall segment is provided at the base of the shaped segment; wherein the base of the shaped segment is provided at the side of the shaped segment opposite to the location of the entrance in the main body, wherein the shaped segment comprises or consists out of a frusto-conical shape, wherein the frusto-conical shape comprises a closing section (123, 232, 323), characterised in that the closing section of the frusto-conical shape is impermeable to premix gas. - a main body; wherein the main body comprises a cylindrical shape; - a porous wall; - a distribution chamber delimited by the main body and by the porous wall, - an entrance in the main body for introducing a premix of combustible gas and air into the distribution chamber; wherein the porous wall comprises a first porous wall segment and a second porous wall segment; wherein the first porous wall segment and the second porous wall segment both comprise pores for the premix gas to flow from the distribution chamber through the pores for combustion of the premix gas outside the distribution chamber; wherein the first porous wall segment comprises or consists out of a shaped segment, wherein the shaped segment is directed to the inside of the distribution chamber, such that when the burner is in use premix gas flows from the distribution chamber through the pores of shaped segment to the inside of the shaped segment; wherein the shaped segment widens in the direction away from the entrance in the main body wherein the second porous wall segment comprises an annular porous wall segment; wherein the annular porous wall segment is provided at the base of the shaped segment; wherein the base of the shaped segment is provided at the side of the shaped segment opposite to the location of the entrance in the main body, wherein the shaped segment comprises or consists out of a frusto-conical shape, wherein the frusto-conical shape comprises a closing section (123, 232, 323), characterised in that the closing section of the frusto-conical shape is impermeable to premix gas. wherein the porous wall comprises a first porous wall segment and a second porous wall segment; wherein the first porous wall segment and the second porous wall segment both comprise pores for the premix gas to flow from the distribution chamber through the pores for combustion of the premix gas outside the distribution chamber; wherein the first porous wall segment comprises or consists out of a shaped segment, wherein the shaped segment is directed to the inside of the distribution chamber, such that when the burner is in use premix gas flows from the distribution chamber through the pores of shaped segment to the inside of the shaped segment; wherein the shaped segment widens in the direction away from the entrance in the main body wherein the second porous wall segment comprises an annular porous wall segment; wherein the annular porous wall segment is provided at the base of the shaped segment; wherein the base of the shaped segment is provided at the side of the shaped segment opposite to the location of the entrance in the main body, wherein the shaped segment comprises or consists out of a frusto-conical shape, wherein the frusto-conical shape comprises a closing section (123, 232, 323), characterised in that the closing section of the frusto-conical shape is impermeable to premix gas.