Tap on filling loop feels really difficult to turn

[elementals]

The pressure keeps dropping down to zero overnight when the boiler is off (there's someone coming round tomorrow to try and locate the leak). In the meantime we're just topping it back up but it's becoming increasingly difficult to open the tap on the filling loop - today it almost feels like it won't open at all and I don't want to force it. What's the reason for this?

Thanks

 

[Rickster123]

You've worn it out

 

[PlumbBobBob]

get the person coming round tomorrow to fit a new filling loop for you