did you replace both valve with copper pipe?
when you let the coolant flow from the header you only have to let a little out then put the top on or there wont be enough in there and it will start to push air round the system which could cause poor heat through the matrix.
also massage the large pipes as the engine warms up on fast idle it will help to push any air out.
are you losing water from the system once the header is sealed?
the 106 temp also concerns me. would say your water pump is on its way out. i replaced mine because i didnt like the 102 i was getting. got one from euro car parts for 40 quid with a new stat. now it runs at 96. much better!
however be prepared to change the matrix after the pump as the new preasure behind a 16 year old matrix can split it.
hope this helps.
