Am I being a bit dense or is it cheaper to buy the whole unit rather than the crown only?
http://www.wickes.co.uk/drayton-15mm-trv4-integral-sensing-head/invt/228625/
http://www.wickes.co.uk/drayton-15mm-angled-trv4-white-head/invt/228624/
http://www.wickes.co.uk/drayton-15mm-trv4-integral-sensing-head/invt/228625/
http://www.wickes.co.uk/drayton-15mm-angled-trv4-white-head/invt/228624/