A fuel cell system comprising: a burner assembly comprising: (i) a hollow longitudinally elongate body extending along a central axis and having a first end and a second end, (ii) a burner wall located between said first end and said second end, and defining a first volume from said first end to said burner wall, and a second volume from said burner wall to said second end, (iii) an oxidant inlet into said first volume, the oxidant inlet for providing an oxidant flow therethrough, (iv) at least one hollow elongate burner abutting said burner wall or extending through an opening in said burner wall from said first volume to said second volume and comprising: (a) a burner plate or mixer having a first side opening into said first volume, and a second side opening into said second volume, (b) a first fuel inlet into said first volume for feeding a first fuel from a first fuel passageway to said first volume; and, (c) a second fuel inlet into said second volume for feeding a second fuel from a second fuel passageway to said second volume; wherein the system further comprises at least one connection for selectively connecting the first fuel passageway to the second fuel passageway for delivery of a mixture of the first fuel and second fuel to the second fuel inlet. a burner assembly comprising: (i) a hollow longitudinally elongate body extending along a central axis and having a first end and a second end, (ii) a burner wall located between said first end and said second end, and defining a first volume from said first end to said burner wall, and a second volume from said burner wall to said second end, (iii) an oxidant inlet into said first volume, the oxidant inlet for providing an oxidant flow therethrough, (iv) at least one hollow elongate burner abutting said burner wall or extending through an opening in said burner wall from said first volume to said second volume and comprising: (a) a burner plate or mixer having a first side opening into said first volume, and a second side opening into said second volume, (b) a first fuel inlet into said first volume for feeding a first fuel from a first fuel passageway to said first volume; and, (c) a second fuel inlet into said second volume for feeding a second fuel from a second fuel passageway to said second volume; (i) a hollow longitudinally elongate body extending along a central axis and having a first end and a second end, (ii) a burner wall located between said first end and said second end, and defining a first volume from said first end to said burner wall, and a second volume from said burner wall to said second end, (iii) an oxidant inlet into said first volume, the oxidant inlet for providing an oxidant flow therethrough, (iv) at least one hollow elongate burner abutting said burner wall or extending through an opening in said burner wall from said first volume to said second volume and comprising: (a) a burner plate or mixer having a first side opening into said first volume, and a second side opening into said second volume, (b) a first fuel inlet into said first volume for feeding a first fuel from a first fuel passageway to said first volume; and, (c) a second fuel inlet into said second volume for feeding a second fuel from a second fuel passageway to said second volume; (a) a burner plate or mixer having a first side opening into said first volume, and a second side opening into said second volume, (b) a first fuel inlet into said first volume for feeding a first fuel from a first fuel passageway to said first volume; and, (c) a second fuel inlet into said second volume for feeding a second fuel from a second fuel passageway to said second volume; wherein the system further comprises at least one connection for selectively connecting the first fuel passageway to the second fuel passageway for delivery of a mixture of the first fuel and second fuel to the second fuel inlet.