System for fastening ignition spark plugs (2) of boilers or the like, comprising a supporting plate (1), which supporting plate (1) has at least one insertion hole (11) intended for the insertion of a spark plug (2) and/or of an inspection window (6), which spark plug (2) comprises an outer ceramic tubular body (21), inside which a detection and/or ignition rod (22) is housed which projects at least from one head end of said ceramic tubular body (21). Said insertion hole (11) having such dimensions that said spark plug (2), in the inserted condition, forms a gap region between the outer surface of the tubular body (21) of the spark plug (2) and the inner surface of the insertion hole (11), at least in said gap region there being provided means (4) for fastening and sealing said spark plug (2) to said supporting plate (1). Said fastening and sealing means (4) are composed of glass material (4) which is brought in the liquid or semi-liquid phase beforehand such to adhere mechanically and/or by chemical/physical adhesion to the outer surface of said tubular body (21) of the spark plug (2) and to the inner surface of said insertion hole (11) and subsequently it is brought to the solid phase.