It sounds as though you didn't "discuss" your situation with the plumber upfront. You've just begun making payments on a $2,000 bill, when the plumber fully expected payment in full.
The plumber has expenses. He has materials to pay for, workmen that he employed. He's out of pocket a certain amount (let's call it $1,000, just for the sake of argument), and you've sent him a few hundred dollars. He's working on negative cashflow, and I understand why he's inclined to put a lien on the property to assure himself that he'll get paid.
Talk to the plumber. Offer him some "incentive" to go along with your "payments". Set up a payment schedule that's agreeable to him, and make sure that you add in some "interest" to make up for the lateness of "full payment" or perhaps even a "late fee" of some sort. And then stick to that schedule.
I applaud your efforts to pay off your debt... but clearly, at least so far, the plumber isn't on-board.