Hairline cracks on a new floor

[Kevbos]

If grout cracking .tiles still stuck .then grout is the problem. If cracks in grout are around every tile .then too much water in grout ,if cracks only on certain areas then subfloor has shrunk .grout gave way .this suggests heating turned on too early .every floor i do with underfloor heating .i tell client 4 weeks before heating goes on .then lowest setting .it must stay at that regardless for 2 weeks .then turn up a couple of degrees weekly..as we can never know what they actually do .