Indesit CS1265WG continuously on

My Indesit CS1265WG fridge/freezer is running continuously – the compressor does not have inactive periods. There is a build-up of ice at the back of the fridge. I conclude that the thermostat has failed. If I can obtain a suitable replacement thermostat does the phial (or capilliary pipe) just feed into the cavity between the top of the cabinet and the top of the fridge compartment or does the pipe have to be routed around anything, possible a thermostat sensor disc? I am prepared to change the thermostat but imagine that a sensor disc would be difficult to access and the combined cost of the spares would make a replacement fridge/freezer a more sensible option.