Why is it that the gas cooktop burners of my new Hotpoint Ultima HAG60P Gas Cooker make a continuous hissing sound when on? Is it something to do with the gas pressure because every time I ignite either the oven, grill or hobs it gives off a gasey smell. It could be that the pressure of gas is greater than it should be.

sumaira, May 2020

Gas pressure as such shouldn't be a problem if you are using natural gas from the street pipeline. The issue is more likely to be the gas to air mixture ratio, especially if you are observing yellow or orange tips to the normally blue flame on the burners.
There is a method to adjusting this gas to air mixture ratio, at the the open tube under each burner but I suggest it is left to a qualified engineer to perform this adjustment, albeit it very simple and quick. It may be a case of built up dirt from spills or cleaning that has slightly restricted the air flow.
(If you did chemistry at school and remember using a bunsen burner, that little metal sleeve that covered the hole at the bottom which adjusted the flame from yellow to blue is the same method that your hob uses to keep the flame blue..)

Rupert, May 2020