Garden tap low pressure and hissing

[countryman]

I’ve just noticed my outside tap is making a sort of hissing sound and the pressure doesn’t seem as good as it was. It has much less power coming out of the hose pipe. A few months ago the return valve was fixed as it got stuck could it be related to this? I’m happy to try taking it apart to see if anything looks amiss but not sure how to turn off the flow to it. Would I likely have to turn off the whole mains water? I have a handle under the sink near where it goes through the wall but not sure if that makes a water turn off or not… really don’t know anything about plumbing but happy to try if it is something simple to save another visit!

 

[ShaunCorbs]

Would say the non return valve in the tap has a problem

 

[rocketmanbkk]

Put a new tap on

They’re only cheap

Job done I’d say