my hatch was blowing hot for a couple of mins then going cold,blowing hot out 1 side car and cold out the other,best way to sort it is buy a no spills funnel from ebay,then put heater to hot ,dont put fan on at anytime while doing it,fill funnel half way on header tank,start car let it idle see if any bubbles rise up in funnel,burp your top radiator pipe,let thermastat kick in a couple time,look see any more bubble,have feel see if its hot and stays hot try fan and see if its red hot then also.if that dont work it could be crap blocking somewere,get a flush in it,this work't on mine,coolant colour dont matter as long as its right coolant,mine is pink as well.you could even try flushing heater out,pump coolant threw it the wrong way sould remove any crap in it.i can say their a nightmare to get air out i found out,but with no spills funnel its easy.if none of that works then i would say do as salsa-king said take it back let them sort it.