The underfloor heating in the bathroom is controlled by the thermostat in the bathroom, which in turn is connected to the unit as shown in the picture:

This is placed in the white cabinet in the laundry room or in the hallway. If the heating elsewhere is working, such as the convector in the living room, then it is overwhelmingly likely that it is this unit that needs to be replaced to restore heat in the bathroom.

Contact Stavanger Installasjon on phone 51 84 63 20, preferably Gaute Li, as they have experience with these units since the building was new.