The release/drain faucet spout for my boiler is dripping and the knob won't stop. It turns both ways!?

The spout comes out the side of the boiler. I can turn the knob so it's just dripping, but if I try to tighten further (turning to the right) it loosens and just keeps turning and the water comes out again. The is a Peerless gas boiler that about 7 years old.