Decided to have a crack at replacing the sensor as it seems like a 2 min job, however being a complete noob, my brain was frazzled after opening the engine cover. Is the green thing in the photo the sensor? Any help would be appreciated, cheers.

First Welcome to the forum.

 

That "Green" thing is the oil pressure switch, the coolant temp sensor will be on the thermostat housing, if you follow those thick rubber pipes back you will find the thermostat housing and it's #8 on this diagram https://volkswagen.7zap.com/en/rdw/polo+derby+vento-ind/po/2005-461/1/121-121075/#8 

5 hours ago, nige8021 said:

First Welcome to the forum.

 

That "Green" thing is the oil pressure switch, the coolant temp sensor will be on the thermostat housing, if you follow those thick rubber pipes back you will find the thermostat housing and it's #8 on this diagram https://volkswagen.7zap.com/en/rdw/polo+derby+vento-ind/po/2005-461/1/121-121075/#8 

Thanks for the welcome and reply! Will have a look tomorrow morning, hopefully better luck next time.