D
Deleted2797112
Here are details of the heater:
https://www.towelradiatorstore.com/600x1500mm-Stainless-Steel-Towel-Radiator-Polished.html
If you follow the links on that website to the installation instructions for electric only, you'll get this.
Extract:
"The electric heating element must be inserted into the towel radiator vertically through one of the entry points at the bottom (right or left). The second entry point on the bottom is then sealed off with a blanking plug. You will then need to fill up the radiator with water or water/glycol (90/10) in order to stop the water from freezing (if necessary) using the third inlet/entry point on the top of the radiator. Please leave a 2-3cm gap from the top of the towel radiator when filling it up in order to give some room for the expanding hot water. Fasten the blanking plug and air valve to the other top inlet point. Your heating element can then be connected to your power supply. Once the heating element is turned on and has heated the towel radiator, please bleed the towel radiator at even intervals. This ensures that there are no air gaps inside the pipes and that the towel radiator can reach its maximum heating capacity.

The heating element must never be turned on unless the towel radiators is filled up with water and fully submerged. Otherwise it will burn out and this will invalidate your product warranty."