Noises in and from the radiator and heating system.
Splash and blop sounds
Accumulations of air in the radiator are showstopper when the heat needs to be circulated in the system. Air in the radiator can typically be identified if one end of the radiator is hot while the other end is cold. The cold end probably has an air pocket somewhere. Another sign of air in the radiator may be that the radiator is making splash and blop noises.
When the radiator is to be vented, turn the vent valve counterclockwise. Remember to have a cloth or tea towel ready. If air comes out first, wait a moment and leave the valve open until water comes out. When water starts to come out, the radiator is vented and the valve can be closed again by turning it clockwise. If no water comes out, fill the heating system with water.
Remember to restart the circulation pump after venting.
Hissing in the pipes
The problem can be remedied by turning down the circulation pump speed. You do this on the pump itself. Older models run at excessive speeds, which is not necessary at all in smaller homes. New circulation pumps run at a lower speed and many can regulate the speed themselves according to the needs of the system.
It knocks fast and can sound like a machine gun!
This type of knocking noise often occurs if the return flow is reversed or if the radiator valve is reversed and installed incorrectly. The water therefore runs the wrong way through the radiator valve and it can not close properly. The water flow causes it to open and close very quickly, which sounds like shots from a machine gun.
It knocks and clicks slowly.
When iron and steel get hot, it expands. It could also be because the radiator expands in the brackets its mounted on. If the sound originates from the brackets, our experience is that knocking and clicking sounds occur because the small plastic protectors on the brackets are missing and have not been installed. As soon as they are installed, the knocking and clicking noices will stop.
Knocking noises can also occur if the heating pipes are in tension or rubbing up against something - e.g. in a floor separation. As an experiment, you can remedy this by giving the pipes a little more space. If they are uninsulated, you can advantageously try to insulate them to attenuate the sound and the frictional resistance. If the problem persists, professional help must be called.