Is this just a hob only set into the work top?
Can you post the model number please.
If you open the oven door there will be a sticker in there with the model details.
Thanks for that ive got it now.
Im afraid the answer is no you cannot replace just the hob top as its all one unit in there. The hob is part of the complete oven on this.
But you can replace the parts on there. If you say they are not heating up as well then its more then likely the regulators in there. This is the part you turn to turn the hob on. This contols the heat on the hobs so they can actually be replaced. But if you need all of them and you have to get an engineer in then you will be cheaper to get a new oven as these kind of ovens are not that expensive compared to other as you can get a new Hotpoint for about £260.