<<KABLANG!!>> at heat up, cool down

307TurboFire

As of last season, a historically very quiet system is making loud noises. No change to system. One radiator, or a pipe leading to it, is routinely making a series of sometimes very loud KABLANG!! sounds as the system heats up. I do not believe this is water hammer for three reasons: 1) the pitch seemed to be OK to begin with, and I have increased it now twice, it definitely breaks the level bubble; 2) It tends to happen with a certain timing with a period that gets quicker as the system heats up, other radiators are also making some unusual POINGG!!! sounds, but not nearly as much; 3) I have heard the one radiator that goes KABLANG!! make the sound long after the boiler is off, I think as much as 30 minutes later, as the system cools down. I am using the default brand of vent, the vent is relatively new, but maybe I should change that? All of the vents are less than 4 years old. It it some kind of vacuum issue when the steam wave front collapses? Why would it happen after the boiler is not even firing and probably has not been making steam for some time? What can be done?

KC_Jones

It's expansion noise. Something is rubbing against wood and causing the noise when the metal is expanding (heating up) and contracting (cooling down) long after the boiler has stopped firing.

AdmiralYoda

How clean is your boiler water? I have only experienced a Kablang once, my boiler water was dirtier than usual and my poor near boiler piping sent some water up the main. It is called surging. I drained the boiler, flushed it out a bit and it hasn't happened since.

How much does the water level go up and down in the site glass? Shouldn't be more than 3/4" or so.

Jamie Hall

What's hung up on the piping? If the noise or anything like the noise occurs that long after the boiler is off, it's expansion -- and a really loud single whang suggests that somewhere along the line something is really restricting the movement of the pipe.

307TurboFire

I appreciate the feedback. The boiler water seems pretty clean both in the sight glass and after I have drained a cup or so monthly out of the bottom bibbs. It gets regular maintenance, and I routinely check the pH, it's neutral.

The boiler was surging for the first year plus after install and had to be skimmed a few times, I guess for manufacturing grease. Also used some SurgeX for a while, but have not added any since year one. I have not seen much bouncing in the sight glass since year three. I was thinking either wet steam or thermal expansion and contraction.

Since I heard it when the boiler was off, I guess it must be both thermal expansion and contraction. I cannot imagine what could be binding the pipe at this point. It never made a sound like this from 45 years ago until 2022-2023 season, there has not been any kind of intervention anywhere near the area, and there are no signs of settling or anything like that.

EdTheHeaterMan

Buildings settle over time. More rapidly just after building them, and after 2 years or so, that settling can be very slow. Depending on what the foundation is on, Bed rock, Clay, Sandy soil, underground water movement, The home may have settled to a point that there is a noise that has increased to a point that it is really loud. You just need to keep looking at every pipe, main, return, riser, and swing joint to see if it is binding anywhere. As the wood flexes over time and the metal pipes stay rigid, there will be noise. KABLANGs are much different than KABOOMs but you can usually solve both with some sort of plastic bushing or glide path wedged between the wood and the pipe. We have made them from cutting up a plastic gallon milk bottle for KLABANGs and 1/2 gallon milk bottles for KABOOMS.

Hope this helps

dabrakeman

Could be a hanger. I suspect such in my house but just have never had the motivation to get the experimentation going. In my case about one to two hours after the heat goes off at night I get a pop that sounds like the worlds largest door knocker. In emanates from the area above the boiler. I think it is likely that it could be about where a slot bar hanger holds the main only a few feet from where it turns away from the boiler and thus could see a shift in vertical force as the near boiler piping contracts and expands. It attaches to a soft wood main hallway floor. This hangar was put in place when the boiler was replaced over 10 years ago. Probably been doing this for at least the last 5 or 6 years. If you suspect a hanger near the boiler perhaps you could try tightening or loosening it slightly (I think I am talking to myself😄).