Ok Update spoke to Fiat and log a support request. The heater will only work when engine is running, so heater pad to be fitted when parked.
Hope this help any one else in the furture. My ducato 250/290 its on a German spec Van. So please for this as the uk isnt deemed cold enough for this feture.
Giles
Fiats reponce after giving Vin number:
The urea system fitted to the vehicle / chassis supplied, we can confirm has electrical systems for heating the tank and pipes so to prevent the AdBlue freezing (freezing point of about -11°C).
It is also equipped with a return pump to extract the fluid from the pipes, returning it to the tank and thus preventing freezing of any fluid left in the pipes.
If you require any further assistance, please reply to this email or contact us by calling Fiat Professional at 0080034281111 .
Yours sincerely,
Customer Care Stellantis EMEA Fiat Professional