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Our ancient boiler finally bit the dust, so we hired Keyspan / National Grid to replace it with a Burnham IN6 gas-fired steam boiler, for our one-pipe steam heating system. We have a four-story townhouse.

The original system & the radiators seemed to work fine without any troubles until now. For reference we used Size No 4′s air valves on the 1st floor, increasing to Size D on the top floor.

Three of our radiators have sprung leaks since the new boiler has been installed. They hiss & whistle and water burbles from the air valves, and now water is also leaking from the pipe-to-radiator connection as well.

So the installer reduced the pressure from 5 psi to 3 psi, but this hasn’t stopped the hissing and leaks. They said the radiators were not in their scope of work, and suggested that I should hire another plumber to correct the problem.

The manufacturer literature for Burnham cites numbers like 0.5 psi to 2 psi, so the 3 psi to 5 psi range that Keyspan used seems high. Could this be forcing steam out of the radiator pipes in unexpected ways? Am I even comparing correct numbers?

I am going to try replacing the air valves with new ones, but I need to know why the radiators might be leaking. Before I call in another plumber, any suggestions what may be going on?