Tim Lamb wrote:

The underfloor heating pipes should not run under the kitchen units
anyway.

Is that relevant? The part of the flooring which might need to be drilled
is not under the kitchen units and so has the UFH pipes directly beneath it.

I guess your floor fitters used a butt joint instead of the tongue and
groove supplied.

I don't see how that can be the case, since the depression occurs only over
one small part of the entire length of the plank.