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Loud cracking sound at one lower floor baseboard radiator

We live in a 33 year old home with perimeter baseboards, they are the standard one pass copper pipe with aluminum fins all with kick plate and adjustable vent on top. There are 4 zones, 2 up and 2 down. We bought the place about 6 years ago and replaced the original cast iron boiler and separate DHW tank with condensing boiler (on outdoor air reset) and an indirect tank. It has worked well and was really quiet although it doesn’t really condense much due to the higher temperature requirements of the distribution system.

About one year ago the DHW circulator packed it in, so I picked up a new circulator and replaced the faulty one. It has been a few years since I was on the tools but this went ok and everything was back working ok a day later. Shortly after we started getting these extremely loud banging sounds almost like the crack of a whip coming from one of the down stairs radiators. At first I thought it was maybe heat related expansion creating and releasing pressure so I cut a tiny bit of the new engineered flooring that seemed to be tight up against the copper riser pipe to the radiator, this didn’t help. I have opened the bleeder a few times and just straight water comes out not even a hint of air. I tried turning the pump from medium to low speed but no real change.

The cracking sound is definitely coming from the radiator in the front entrance way on the ground floor or in very close proximity to it. The sound started right after the circulator was replaced. This sound seems to increase with boiler temperature, so louder when colder out. There are usually 4 or 5 loud cracks in a period of 3 -4 minutes starting just after the zone valve opens or when the pipe starts getting hot.

The house has two floors all above ground, the ground floor is concrete with tile in most areas and floating engineered floor in our entrance way where the noisy radiator is. The upstairs floor is a concrete skim coat and tile with engineered floor over it. We live in Vancouver so the noise is a problem for about half the year during heating season. I put up with this for a part of last winter and hoped it would just go away but it didn’t. It has now persisted for just over a year and is still so loud it wakes me up at night.

I am not sure what to do or where to look? The boiler is only accessed from the suite downstairs which is rented out so it is hard to get in there and really investigate as much as I would like. The offending radiator is in our space. If it was in the tenants space they would have complained or moved out by now.

Any ideas?


  • Jamie Hall
    Jamie Hall Member Posts: 23,286
    It sounds like an expansion noise. It may have started with the new circulator possibly being able to bring hot water to the unit faster than the old one. Or it may be coincidental...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • icesailor
    icesailor Member Posts: 7,265
    You describe a sound like "Cracking A Whip". That sounds like Snappy noise. Is it a "Snap" or a "bang". Snappy noises usually make me think of water expanding into steam. Because the noise started after you replaced the DHW Indirect pump, is it possible that the DHW pump is smaller and the boiler is making steam? Usually, if something worked, and suddenly stops etc, what changed?

    Especially if the snappy radiator is the first one on the supply side of the boiler.

    Something to think about.
  • 4Johnpipe
    4Johnpipe Member Posts: 480
    edited February 2015
    Are the baseboard emitters nailed to the studs / wall or are they screwed? Not sure what part of the country you live in...we have had some record cold and you may be experiencing a coincidence with the cold exterior wall and a metal baseboard housing moving and "snapping" along a nail or a loose screw as the enclosure heats up. the DHW circulator should not have had an effect on the system heat circulator...Just a thought...
    Considerate People, Considerate Service, Consider It Done!
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