The switch trips the relay, hence switching the fans on the relay has a permanent live and it will be either a switched live or another permanent live (Fans will run without ignition if the latter) the switch would be in the rad or thermostat housing, not in the block, unless something unique to the ST?
The Escos has a two stage switch so not sure how this works I would imagine there is a high speed and a 'Low' speed relay.
I would check the relay and if good the switch must be suspect to test bridge the connections and see if the fans run.
Martin