I have an Ariston micro genus combi boiler G.C.N. 47-116-14 . When I turn on the water tap the boiler does not light and the yellow l.e.d. just above the on button lights up, the book calls it the "fume sensor" l.e.d. I cannot find a sensor in the machine. The fan is running ok. Anyone know what causes the fume sensor l.e.d. to light and stop the boiler lighting. many thanks for any replies.

Ken, November 2013