Floor tiles grout crack and uneven

[vivimimi]

DIY Advice needed

Last year we put Underfloor heating and put new tiling for the entire new extension. After using for 1 year, I noticed cracks amongst one set of tiles. Looks like one tile is higher than other three neighbouring ones. The grout is also cracking.

Any experts in this forum could provide some light. I'm thinking to add new grout on the cracked grout, but not sure what to do with the uneven tiles.

Any help or advice really appreciated.

Does the raised tile rock at all or is it solid , stable?

all the tiles are stable, none are rocking

Do you have any spare tiles?

Is the opposite corner of the tiles sunk compared to its neighbours?

Tile not tiles

@tanstaafl - I may have extra tiles. But other ends are all ok and at level.

Seems like something has pushed up that corner of the tile ( rather than an uneven lay which would be indicated by the opposite corner of the tile being lower ) plus you say it doesn’t rock.

It could still be an uneven lay if the rest of the grout around the tile is holding it in place in the opposite corner.

If you tap around the tile with the handle end of a spoon, does it sound consistent across the tile , or hollow anywhere?

Taking the tile up and addressing the underlying issue is the long term solution ( which is why I asked about spares ), in the meantime I’d wait.

I say wait only because putting new grout in and having the underfloor heating on seems to be contradictory to me.
But maybe there’s grout that sets just fine with underfloor heating on.

What was the tilers advice that laid the floor OP? I assume you would have spoken to them. We had problems with a tiled floor in our bathroom, grout cracking etc, to be honest I wouldn’t choose to have tiled floors again.

thank you @tanstaafl for your assessment. The spoon tap test is not showing any hollow places around.
@Roselilly36 I will talk to the tiler today and seek their advice.

I have a feeling whether the other tiles make have actually sunk. The three tiles are on the part where we had extension. The floor is created by wooden grid (see pic).

That makes sense, some give the the wooden floor perhaps? This was the same situation with the tiles in the bathroom, tiled over floorboards. I have (existing) tiles in my new home they seem ok, as they have been tiled on a concrete floor in the extension. I hope you get it sorted out.

thank you all

it looks like the subfloor is chipboard on wooden joists.

Is this in a room that contains water, and could it be leaking?