The present paper describes atmospheric experimental tests of a new Ansaldo Energia full scale burner which was designed to burn fuels byproduct of steel making processes (mixtures of Blast-Furnace Gas (BFG) and Coke-Oven Gas (COG)), characterized by very low heating values (LHV∼2–3.5 MJ/kg) and very low stoichiometric air/fuel ratios (∼0.5–1 kg/kg). In particular, flame stability and blow-out margins were assessed for different burner variants and fuel compositions such as pure BFG, blends of BFG with increasing content of COG, and also a synthetic mixture of natural gas, hydrogen and nitrogen (NG/H2/N2). Except for pressure, all burner inlet conditions were simulated as in the actual gas turbine engine. The best performing burner among those tested demonstrated an excellent burning stability behavior over a wide operating range and stably burned pure BFG without any supplementary fuel. Furthermore, considering that in most operating concepts gas turbine engines for Ultra-Low BTU applications require a back-up fuel (such as oil, propane or natural gas) to ignite and ramp up or to perform load-rejections, the present atmospheric tests also assessed maneuvers to switch from natural gas operation to syngas operation. Also in this type of dual-fuel operation the burner demonstrated a wide flame stability range.