Electric cooker, random operation

[Santorium]

Hi,

My (admittedly old) electric cooker is playing up. Sometimes it works fine, but on other (seemingly unpredictable) occasions, it fires up (either hobs, grill, or oven) fine but dies after a few minutes.

At other times, the hobs/grill don't get up to full temperature and the oven doesn't work at all!

Any ideas, aside from "go get a new one"?

Thanks in advance.