Dimplex instruction manuals are on the web.
For one example here
And the instructions say
The peak supply must be connected via a switched fused spur with a fuse rated suitably for the appliances flex, the off-peak supply , via a 20A double pole switch. Failure to follow these instructions will mean that the manufacturer?s instructions have not been adhered to. THERE ARE NO EXCEPTIONS
? This heater must be earthed ? Not suitable for connection via a plug top ? Do not locate the heater immediately above or below a fixed electrical point i