I have the same type system and while I am no expert it does sound like air in the system.
Do you also hear gurgling?
I installed "float" type air eliminators on several of the base board radiators and this has helped tremendously.
If this is a new recent problem then air must be getting in when the system cools down and creates a vaccum. The expansion tank may need to be looked at. I'd have a Pro come in...it's probably worth it in the long run...

I'm experiencing the exact same problem. Our problems first started with gurgling and that was it. The plumbers bled the pipes, and that's when our problems began with the vibrating (or knocking, as we call it). The knocking is so bad, that we can't even sleep at night without turning the heat off. It starts off as a slow knock, proceeds into an extremely rapid knocking, and then returns back to the slow knock before stopping; the episode lasts for about two minutes and happens every time the water circulates.

The pipes have been bled four times, and the plumbers have even installed an in-line air bleeder. The in-line air bleeder solved the gurgling problems, but the knocking persists. The knocking has even appeared in different places throughout our home (about every 2 weeks or so, new knocking appears). The colder it is outside, the louder the knocking is.

The plumbers have said that this is normal (caused by the expansion of the pipes as the hot water circulates through them) and to be expected with this type of system and a new house as it settles (the house was just finished this past July), but I find that extremely hard to believe, because if that were the case, I KNOW that no one would ever have hot water baseboard heating installed! Who could tolerate it? We're very much at our wit's end with this problem; if anyone has any ideas, we'd be more than grateful if you could share them with us!

Thank you for any help, and Happy Holidays!

While it is true that the baseboard itself will expand and contract, the usual cause is that the installation is too tight. The pipes need to be able to move to accomendate for this expansion. Also make sure that the water temp on the boiler does not exceed 180*f. Although you can go higher, 180* is fine. As for vibration in the lines, make sure that the pressure in the boiler is about 10psi. "0" psi on the boiler is not good and means that the automatic fill valve is stuck. Also make sure that the pump is running. It is also helpful to add a teflon base to a boiler every 5 years or so. FOR new installs, make sure that the boiler was purged totally with water. solder, flux and dirt need to be cleaned out of the system.

Hope this Helped

While it is true that the baseboard itself will expand and contract, the usual cause is that the installation is too tight. The pipes need to be able to move to accomendate for this expansion. Also make sure that the water temp on the boiler does not exceed 180*f. Although you can go higher, 180* is fine. As for vibration in the lines, make sure that the pressure in the boiler is about 10psi. "0" psi on the boiler is not good and means that the automatic fill valve is stuck. Also make sure that the pump is running. It is also helpful to add a teflon base to a boiler every 5 years or so. FOR new installs, make sure that the boiler was purged totally with water. solder, flux and dirt need to be cleaned out of the system.

Hope this Helped

Make sure the boiler water temp is at 180*f, and that there is about 10 psi pressure on the boiler. The knocking you hear is the pipes expanding and is attributed to the base being too tight. You need room for expansion. On new installs, the boiler should be flushed with water to remove all dirt and solder crap. A teflon base boiler treatment is availiable and helps most situations.

Make sure the boiler water temp is at 180*f, and that there is about 10 psi pressure on the boiler. The knocking you hear is the pipes expanding and is attributed to the base being too tight. You need room for expansion. On new installs, the boiler should be flushed with water to remove all dirt and solder crap. A teflon base boiler treatment is availiable and helps most situations.