Hi Kate, The problem appears to be the manufacturer of this fitting. The lamp it says you need to use is a 28w 4p which you have done. However this lamp should not be used with a starter switch (the round cylinder shape popping out of the body). They are only used with 2pin lamps. This appears to be the problem. Just call our freephone and we can explain further. Is it possible the old lamp has only 2 pins on the back regardless of what that sticker says on the fitting? If so you need a 2pin 28w version.