We present the results of pilot-scale testing of the thermal polymerization inhibitor Dewaxol 3002 under elevated operating temperature conditions. The reagent, synthesized based on heterocyclic compounds and an aromatic amine, was utilized in the unit for separating heavy fractions from pyrolysis gas for an EP-60 ethylene plant. It was established that the inhibitor is high-performance and the runtime between repairs was lengthened for boilers damaged by clogging due to polymerization of heavy unsaturated components of the pyrolysis gas.