Thanks for link, expect I’ll get some.  For now I used one of the other brass ones as it was easy to get, but I’ll get pressure rated ones - it’s annoying when stuff breaks.

The outdoor ground loops and the indoor rad system both have header tanks - so there’s no pressure to speak of by the way. 

I’ve been running with 3 groundloops for a couple of days rather than the usual 4, the system has to try a bit harder and the heating COP dropped from 4 to 3.7.  This is the worst time of year for the cop - the ground is cold, even though the air is starting to get warmer. 

Dezincification?

Uhhhh, it happened again the other day.  That is, another brass coupler cracked for no obvious reason (which I guess means fatigue failure after 3 years of 15C ish hourly temperature cycling), a litre or two of water+(non toxic) glycol came out, and the heatpump stopped.  Took me a day to notice (there’s lots of insulation at our house), Mrs RobL didn’t notice at all (even tho she’s sensitive to the 🥶 ).

I had already bought enough of the plastic 6bar rated fittings, so I’ll change them all over this weekend rather than one at a time as they fail…

Of the eight 3/4“ hose tails for our gshp groundloop connections, two had completely failed within three years, and four were showing visible signs of a crack forming.  They’re all replaced with plastic now 🤞🏽