Overheating

Car runs ok (temp) while moving at urban road speeds but will go quickly to 100deg plus when sitting for more than 30 seconds at a stop. The temp remains at 100plus for roughly 30 seconds more before the fan appears to start and the temp reduces to just over 90 deg. I have changed the fan resistor module (burnt out) and both fan relays and the thermostat but the issue persists. I have two temp sensors (thermo housing and cyl head) and now suspect either the cyl head sensor as this controls the ECU and drives the fan !!! or the fan, as it has a clutch (I think) which may be dragging:... advice greatly appreciated as I am off on a 600 mile trip very soon...