White paint turning yellow

[bigchicken]

I painted the skirting boards and window sills in two rooms in a new (6 month old) apartment about 2 months ago. I used the crown pure brilliant white non drip gloss. It went on fine and dried pure white. However I have noticed that the white skirting boards now look yellow rather than bright white. Its much worse in one room that the other. The bathroom (which has no windows) is very yellow, whereas the bedroom is a little yellow in some places but has stayed bright white on the window sills.

Could this be caused by the heat in the room? Is there anything I can do about it, are any types of paint better? Or if i put on an undercoat first would that help?

Any tips appreciated!

 

[BOXtheFOX]

I have found different quality of paint in some of the Crown tins of brilliant white also. I changed to Crown Solo and it appears to have solved the problem with the white staying white longer.