Whistling noise from loft tank

[JellyBeanJB]

Loud whistling coming from the tank in the loft when refilling after valve was replaced a Plumber advised it is normal with a new valve and will improve over a few weeks. I don't understand why or how. Is this normal? It is very noisy! We hear it two stories down as loudly as in the loft. Help! Any insights very welcome..!

This could be one possible reason:

What is the difference between a High and Low Pressure Ball Float Valve - On-Demand Supplies (ondemandsupplies.co.uk)

If you have high water pressure, and the plumber has fitted a valve intended for low water pressure, this could result in excessive noise or 'water hammer'.

Thanks! Maybe that's it but how to find out without paying for a plumber again?

You'd have to climb up there and have a good look yourself to be honest. When you're sitting right next to the valve it should hopefully be apparent.

Is this the valve to mains or the float valve that is low pressure / high pressure? I was told the float valve is making the noise

Thanks! (Pressed send to soon!)

It's the float valve, also known as ballcock valve. There are some examples on this plumbing supplies web page:

Ballcock Valves / Ball Float Valves (stevensonplumbing.co.uk)

Thanks