Are those cheap (B&Q, etc) white plastic push-fit end-caps reliable on
15mm copper pipe in a gas-fired domestic central heating system? I
just removed a radiator and used these to cap off the feed and return
pipes. I was alarmed when I saw how easy they push on and pull off by
hand. Has anyone known one to work loose? The pressure of my system
goes up to 2 bar.

Thanks..

Al