The present invention relates to isolated polynucleotides encoding novel PY peptides, and to isolated PY peptides and functionally equivalent fragments thereof. Control means for gas burners are used for supplying a gas flow and a combustion air flow to a burner. A first lever is associated to the first kinematic chain and a second lever is associated to the second kinematic chain, said first and second levers interacting with one another during the opening operation and being equipped with blocking devices in the event of welding of the contacts together.