CH pump leaking even after replacing

[Mjward]

I have a Grundfos pump attached to my UFH manifold. Noticed the floor boards below were warping and that it had been leaking ever so slightly for some time. Removed it, cleaned seals etc, tightened back up, leaked.

So bought a replacement (UPS3), with new O rings and it leaked again. Retightened this time adding a bit of Fernox to the thread but it still leaked.

Thinking potentially the threads on the female brass ring have gone (maybe from over tightening over the years) but any other ideas?

 

[ShaunCorbs]

Is it definitely leaking from the threads any stuff on the face of the brass ?

 

[Gasmk1]

Did you make sure brass faces were clean if first pump had card washers could be some crud stopping it seal

 

[Mjward]

Did you make sure brass faces were clean if first pump had card washers could be some crud stopping it seal

Yup all cleaned. I replaced the brass nuts and that seems to have done the trick. Guessing overtightening over the years had worn the threads