Do I need to reapply thermal paste when the cpu is separated from the cooler?

Ethanh100

Honorable
I am planning on buying and installing a new motherboard for my rig, in which of course involves removing the cpu cooler from the cpu itself. When i am putting the cooler back on the cpu on the new board, must I clean both surfaces and reapply the thermal paste, or can I just put a little more on, or can I just leave it as it was with the old paste on it? Thanks so much for answering!
 
Solution
Always clean and reapply the thermal paste when you remove any heatsink. Failure to do so will almost certainly result in air bubbles and poor heat transfer.