circulation pump,also known as run on pump,you should hear a slight humming noise when you turn the engine off,iirc runs for about 5-10 mins. if you look under the bonnet right hand side back of the engine but near the top you should see it,search on the forum for more info. all info you need should be on hear,if not on this short thread,then its elsewhere, take a look in the tech section in the faqs. iirc,the aux heater on a mk2 comes on at 10 degrees,mk1 comes on at 5 degrees. on my old 1 it still came on up to around 12 degrees. if the run on pump doesnt work then the heater wont run.