Grout joints cracking

[Ajax123]

Only reason for grout cracking in this type of floor makeup is movement. Something is clearly moving. What are the floor dimensions. Is there any hollowness in the tiles especially round where the grout crack are. I agree with your suspicion about the 100degrees C although I suspect that is a bit of an exaggeration. It has just got really cold so have they put the heating on at a high temperature causing rapid thermal expansion and thermal shock?? Is there expansion gap around the edges of the floor. If not it could be trying to belly upwards breaking the grout as it goes.

 

[Mattash99]

Alan, something is definitely moving, just can't figure out what is doing it. The tiles are solid around where the cracks in the grout are, there is some form of expansion round the edges as they are under the units and from memory they weren't cut in tight to the walls. It was a slight exaggeration regarding the temperature, but it was extremely hot, it is basically cracked where all the matting is and I guess it's gonna come down to the heating system, is there any way on an electric system to check if it's been used, other than the tiles being hot!!