I don’t care! Stop knocking and let me sleep!
That would summarize my mood at the end of last year, just after we moved from the garden unit up to the 1st floor. I didn’t get much sleep, because something kept knocking, in the bedroom, right above my head.
When the heat came on, the knocks started in one- to five-second intervals and lasted for about one or two minutes. After the heat turned off, the knocking kept going for a while with a single knock about every five to 15 minutes.
No doubt the noise was coming from our hydronic heating system. My first thought was that I got something wrong with a deflection leg on the supply and return line to the bedroom radiator, which runs right next to and above my head.
After two nights of sleep deprivation, I’d had enough. I checked the exact pex tubing location and then cut a hole into the closet ceiling adjacent to the bedroom, just large enough so that I could stick my head through and inspect the deflection legs.
It turned out that the deflection legs worked fine. But where the horizontal pex tubing turned a corner from the ceiling down into the wall, it was firmly pressed against the drywall. (Image below shows the tubing before drywall installation).
The expanding or contracting pex tubing wasn’t sliding across the drywall. There was enough friction for it to jump in tiny intervals – thus the knocks.
I pushed a piece of cotton rag between the tubing and drywall, which stopped the friction, jumps, and knocking. I finally got my first good night’s sleep on the 1st floor.
The end of knocking?
With that fixed, is our hydronic heating system silent? No. We still have some knocking, although it is significantly less obnoxious.
Although the offset bolt is rounded, smooth steel, it again tends to have enough friction to jump rather than slide across the painted drywall. This is only a problem on the longer radiators. If it starts to bother me, I may take a small piece of thin fabric, such silk, and slide it between the offset bolt and the painted drywall.