Hi Katie!
The wall heaters are made by 'Chatsworth Heating'. Their website and details are here:
http://www.chatsworth-heating.co.uk
The model is a Brio Progress Wall Convector. Chatsworth would ref to the timer as a 'programmer'.
You can download the manual for the wall heater here:
http://www.viridiansquare.org.uk/downloads/wall_heater_manual.pdf
Does the heater itself still work? If I were you, I would visually check the contacts between the bottom of the timer and the inside of the wall heater. Try gently vacuuming inside the heater where the timer sits, to see that it is making a connection.
Otherwise, call Chatsworth on 01903 771021 for advice. They are setup I think for trade, but they may be able to point you in the right direction.