Trying to identify my underfloor heating cold tails

[ericmark]

I don’t the think I’ve heard electric tails being called cold before.

That is the normal name.
@flameport has answered most of the rest, there should be a resistance between the cold tails, and also a resistance to earth. The latter above 1 MΩ the former depending on the size of the UFH. It will likely be less than 1 kW, could be as low as 250 watts, so around 200 Ω to 53 Ω this can be measured with a normal multi-meter, the above 1 MΩ needs a meter using at least 250 volts, normal is 500 volts.

I would think a plinth heater would be better. This one, 1.4 kW,

it will heat up the kitchen far faster than the UFH so you can use it only when required. And less of the heat is transferred into the ground, and still heats low down and does not sacrifice cupboard space in the kitchen. There are hydronic (water) types which can connect to the central heating.