Glad you like it!
If you heat up the design and then put all the parts in, some of the hull heat will be transferred to the components through the reactor heat exchangers. They all need to be around 85% heat for the reactor to reach it's intended state. Maybe that's it?
Edit: Haha now I know why I didn't find the URL thingy, NoScript was blocking it^^
Yeah I worked out it was the heat exchangers. I forgot that their job is to make all components they are connected to, whether that be other components or the hull, have an equal percentage "brokenness". As the hull had a lot of heat and therefore brokenness and the heat exchangers didn't have any, they soaked it up presumably until they were the same percent to breaking