What causes this please?

[jpadie]

Hello all

 

This joint is leaking and looks like it's done so for a while now.   As a result the actuator below it keeps sending mixed signals to the boiler!

 

My question is what causes this?  Is it just a badly made original joint/pipe vibrations loosening it or is it the dielectric or brass to copper that is causing an eventual failure (it's possibly been in situ for 50 years now). 

 

I think it is the heating flow.  I'm planning to hunt for a shut off valve, cut the area out, replace the T (the small pipe behind feeds a radiator in a bathroom behind the wall) and replace with a 15mm coming off the main 22 so that I can add another radiator on the same spur;  and replace with soldered connections everywhere   It's not great access though!  

 

If this is the hot water line (I should know but I don't yet) then it's just replace like for like but with soldered connections.

 

All (on topic) advice welcome!