Problem
If the valve is vibrating (buzzing) this is most likely because it is on the out-flow side of the radiator rather than the inflow side.
This was probably not a problem before because the old TRVs where not closing the radiators down because the wax in them may have worn out and the valve was always left fully open.
The vibrating happens because the flow of water should be coming in under the valve when it is on the 'inflow' side of the radiator, and this pushes the valve pin up against the electronic head.
When it is orientated incorrectly the flow is over the top of the valve and there is nothing to stop it closing completely apart from a small spring inside the valve body. Because of this the valve opens and closes at very high speed causing the valve to vibrate and make the noise you can hear.
Solution
There are a couple of solutions to this.
- If the valve bodies are the Danfoss RA-FS type they have a small grey cap which can be rotated 90 degrees and this swaps the flow from under the valve to over the valve, and stops the valve from vibrating.
- If the valve body is not a Danfoss one then you can (as a temporary measure) turn down the lock shield which is at the other end of the radiator, this reduces the effectiveness of the radiator and reduces its ability to heat the room but it may stop the valve from vibrating because there is less water flowing through the radiator.
- An alternative would be to swap the ends of the radiator over so that the valve body is on the correct end of the radiator.