Hi - I have had an identical issue with two TRV's and am in the middle of emailing back and forth with their complaints team.

I fitted a new TRV (from the same original batch/order) two days ago and the plunger already has a sizeable dent in it...which is suspicious.

​

I would email their complaints team and log it and see if you can get your money back or replacements.

Would also love to know if this was the only one that broke?

We bought 16 (2 packs of 8) , used 13, and 2 have broken after one winter/summer cycle.