I have a 1999 Volvo S40 (bought recently). I usually drives at the weekends and for the whole 5 weekdays it is stationed. However even after a 5days period, before starting, when I open the radiator reservoir cap, coolant was very pressurized and even coming out. Also can notice significant coolant lost and need to refill every week.
Finally I took the car to a technician and he did a chemical color test on radiator reservoir. However results were negative and he said there aren't any gasket leaks.
However I'm still wondering, is this kind of pressure build up is normal? even after 5 days? is this a known bug of the car model?

 

"Significant coolant loss and need to refill every week"

Not normal. Find a new technician. Check the pressure at the cap. It should be in the 20psi range.