TRV Groan

[delmel]

I have a noise problem with one TRV. All seems to work, but every time the stat reaches temperature and cuts heating, this one valve makes a very noisey groan, it doesnot do the same when the stat calls for heat again, only on turning off.
Any suggestions

 

[ricarbo]

Might be fitted backwards. Some have an arrow on them indicating flow direction. If the arrow points to the rad, then the pipe it's fitted to should get hot first on start-up, and vice versa. Most newer ones are not sensitive to flow direction, I believe. Some, eg current Danfoss can have the flow reversed in situ, which is neat. Closing down the lockshield could be worth trying, I don't know. If it used to be ok it's time for a new one?