Knocking Aluminum Radiator Problem: Pipes & Thermostatic Valve Issues in 3rd-Floor Apartment

I live in a block of flats, on the 3rd (last) floor. For some time I have heard knocks in the radiator or in the pipes at the thermostatic valve. During the heating season, radiator valves were usually set to 2 or 3 on a scale of 1-4 on the head. In the current season, there is a tapping that is in intervals of several seconds. It's quite persistent, especially at night. When the outside temperature was above freezing, it helped to close the radiators. At the time of freezing temperatures outside, setting to any numbering did not help, tapping was still listening. I called a specialist from the cooperative who said it was the fault of the aluminum radiators. Strange because so far I have had no problem with aluminum radiators. Additionally, he swapped the valves in the rooms, claiming that it might work. However, this did not solve the problem, I even have the impression that radiators are knocking all over the apartment. Yesterday I opened the valve fully for the night, to the max. The knocking stopped. It hummed slightly, but the sound didn't wake me up anymore. However, this is not a solution in the long run, because the CO bill will kill me. In the morning I set the valve to 3 and the knock came back, but it was louder and at longer intervals. He's going to kill himself. Today I have submitted the case to the cooperative again. I don't want to be lowered into the tree again. The heating does not work properly, the question of where the fault or failure occurred. I am only asking for serious and professional answers. Has anyone had a similar problem and how was it managed?

There is such a thing as thermal expansion (of solids) in basic physics at least in my time. Aluminum reacts differently than, for example, a steel pipe, which makes it crackle.
Somewhere along the way, they exchanged something that reacts differently than others to temperature changes or probably changed the heating settings of the power supply to dynamic (they heat less at night and in the morning they give a higher supply temperature or turn on some additional circulation pumps - hence the temperature changes and crackling sounds carried by the installation ).
Physics, physics, physics ... and elementary school.

Thank you for your response. Even if they have "changed the power heating setpoints to dynamic", knocking occurs regardless of the time of day. And knowledge in physics at a basic or even university level will not make me have a quiet night. The plumber should have the appropriate competences in this regard.

What kind of "knocking"? Crackling noise caused by thermal expansion or mechanical "knocking" - as if someone was knocking metal on a radiator?
In the latter case, the cause may be valves and thermostatic heads (I assume you have them). I had such a case once - when setting the flow to the limit of opening, there was a quick and loud knocking in the pipes. The problem was trivial - this valve (Hertz) should be installed on the return, not on the supply. It was mounted on the supply, the water flow through the valve was in the opposite direction, the water circulation was forced by the pump. At the opening limit, the water pressure overcame the valve spring resistance, which caused it to open. Then the pressure dropped, the valve closed and the cycle started from the beginning, providing an unforgettable acoustic experience - especially at night Closing the valve or opening it helped.

I don't think you have all the valves in the wrong position; I don't think the building manager suddenly swapped the power back ... But just in case, check the required flow direction on the valve (there should be an arrow) versus the actual water flow direction.

Mechanical knock. As if someone is knocking on the door

Loker wrote:

What kind of "knocking"? Crackling noise caused by thermal expansion or mechanical "knocking" - as if someone was knocking metal on a radiator?
In the latter case, the cause may be valves and thermostatic heads (I assume you have them). I had such a case once - when setting the flow to the limit of opening, there was a quick and loud knocking in the pipes. The problem was trivial - this valve (Hertz) should be installed on the return, not on the supply. It was mounted on the supply, the water flow through the valve was in the opposite direction, the water circulation was forced by the pump. At the opening limit, the water pressure overcame the valve spring resistance, which caused it to open. Then the pressure dropped, the valve closed and the cycle started from the beginning, providing an unforgettable acoustic experience - especially at night Closing the valve or opening it helped.

I don't think you have all the valves in the wrong position; I don't think the building manager suddenly swapped the power back ... But just in case, check the required flow direction on the valve (there should be an arrow) versus the actual water flow direction.

and how is such a knocking in an old installation with cast iron radiators without thermostats?

I do not know - I described the incident I encountered. There are probably other causes of knocking in the installation - for example, thermal expansion, malicious neighbors ...

Hello, buddy, I suspect you have valves with thermostatic heads, because with small settings such cases occur very often. The thermostatic head reacts to the ambient temperature, according to the settings that correspond to the appropriate temperature, when this is reached, the heat supply to the radiator is cut off for the time until the ambient temperature drops, then the head releases heat and the radiator makes a clatter because it has already cooled down a little and receives a high temperature of the heating medium . I propose to remove the thermostatic head and put on an ordinary knob, the valve slightly closed will heat all the time but you can properly choke it, then the knocking problem will disappear. greetings.

Please unscrew the nut from the thermostatic head. A valve with an embossed dot and numbers from 1 to 6 will be visible. Each of the valves, starting from the first radiator, must be moved with a key in the order 1 radiator 1 range, 2 radiator 2 range etc. and after the problem, not these stupid things from YT