Upgraded from Hub3 to Hub5 and 1Gig speed but Powerline Boosters won't work any more - any ideas?

Was on Hub3 with 500mb speed, now have Hub 5 with 1 Gig speed. The powerline wifi boosters no longer work.

I did a factory reset. Re-paired them side by side in the same room as the Hub5. Connected the larger  booster via WPS to the Hub (don't know if that did anything). But when I moved the second booster to where I need it in the house, and plugged it in, the connection light showed as two solid orange lights for ages and then went off. And clearly doesnt work as the wifi signal is very weak in the distant part of the house.

Any ideas about how to get the powerlines working? or do I need new boosters?