Wunda UFH tiles cracked

[Alskimck]

Hello

I’m in Hampton SW London and have a floor problem. Wunda UFH water heating was installed over a kitchen area that was half boards and half concrete. The tiles over the concrete are fine, but the ones over the other part have cracked.

I’ve lifted one of the tiles up and the adhesive hasn’t stuck to it at all. I’m pretty sure the builder who i can no longer contact didn’t user a prime or the right adhesive. Is it repairable without removing the whole system and is anyone local enough to quote?

The tiles are 61x61x 1

Thanks