Sounds like the thermostat / capillary is kaput.
Spares are available:
http://www.pacet.co.uk/pacetfanspares.php
http://www.pacet.co.uk/pacetfandistributors.php
If I remember correctly, I got my fan and top hose adaptor from SVC, so you could start there, or try someone from the pacer distributors list who may be closer to you.