Have you still got the old fuse?
If so what are the markings on the end caps of it?
If it shows the current rating as T20A and the Voltage as whatever it is e.g 250V, then you need to get a slow blow fuse with the same current and voltage rating e.g. T20A 250V and dimensions and not a standard (aka fast acting) fuse.
If it just shows the voltage and the current e.g. 20A 250V then as long as the replacement fuse has the same current and voltage rating and also the same dimensions so that it will physically fit securely into the fuse holder, then it should work