Suitable floor coverings used with underfloor heating must be allow the heat to transfer through and also must be stable in their construction, so they do not be-come effected by the temperatures involved.
Although UFH will work with most floor coverings, some floor finishes are better than others in both terms of stability and also for the transference of heat, which itself depends on the floor finishes thermal resistance. Ideally the thermal resistance should have a TOG value less than 1.0, but sometimes a TOG value of up to 2.5 is acceptable.