Be cautious with this one. Two things can go wrong causing the motor to stay on.
1) Faulty thermostat. A thermostat is basically a switch, so see if you can by-pass the thermostat to make it send an 'off' signal. If you get no response then its the motor relay or better still use a multi-meter
2) Motor relay switch packed up and continually in the on position. With this fault the thermostat is permanently trying to send an 'off' signal (hence no click) but the relay is not responding.
GB in Wales
March 2013