How difficult is it to replace a heater control valve? on 2006 Chevrolet Trailblazer

We thought (and were told by one mechanic) that the heater core needeed replaced. that wascovered under warranty. The dealer said it wss the heater contrl valve that is leaking. Would that cause the overwhelming smell of antifreeze in the car? Also how hard Is it to replace as this part is NOT covered under warranty.

Asked by for the 2006 Chevrolet Trailblazer
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The heater control valve could cause the problem. Its not to difficuldt to replace... book time 1.8 hours plus the part for about $90.00. It would be unlikey that part would be under warranty on a car that age.