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Single Loud Crack!!! when the steam flows in my one pipe steam system

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My 1920 house with one pipe steam system. Suddenly, in the last year, one of the radiators on the first floor, about 40 feet of steam pipe away from the boiler, has started to give a very loud 'CRACK' in the beginning of the cycle on. Not hammering, but a single loud percussive noise. The radiator is angled down towards the steam pipe. Any ideas as to what the problem is, the solution is?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,635
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    That's almost certainly an expansion noise as the steam hits it. Can be very annoying. Can also be remarkably hard to track down and fix. But somewhere something is trying to expand but being restrained, and the abruptly overcoming the restraint. Once you find it, there are a number of clever ways to relieve the restraint and get rid of the noise.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Shalom
    Shalom Member Posts: 165
    edited December 2014
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    I've got one that does that. One loud "KONK!!" just as the steam starts coming up.

    Check where the pipe goes into the floor. (You may have to lift up a decorative rosette covering the hole.) Is it rubbing against wood somewhere? If so, can it be shifted slightly?

    (Someone in another thread I was just reading here suggested shimming between the pipe and the wood with a piece of plastic cut from a milk container, which would allow it to slide silently.)