A family member has Wickes underfloor heating under a ceramic-tiled floor
and it has ceased to function.

There's power to the fused switch and the 3A fuse is ok, power then goes to
the thermostat but I can't test it any further because the cable's in a
cavity.

The thermostat has a PCB in the detachable front panel but it doesn't look,
or smell, burnt. Any ideas how to test the panel on its own to see if it's
working? Is the next thing to try a continuity test on the heating cable
from the thermostat to rule out a (somehow) failed wire under the floor?

I only understand 'letrics up to a point and then it all becomes wizardry
AFAIC

Si