No water sound when turning filler tap by expansion vessel.

[KenTucky]

Have an Ariston unvented hot water tank in airing cupboard with the red and white expansion vessels and a filler tap. As advised years ago on these forums when I hear that sound that the central heating water needs topping up I usually wait until cold so the gauge goes to zero and top up to 1. Heard the sound a few days ago on starting so went to gauge and it was showing 2 even when cold. So I went to the filler tap, turned it and whereas normally it's like turning on a mains tap in terms of the sound, there was nothing at all as if there was no water supply. All the rads are hot so no air lock evident. Been in house since 2008 and not had this experience before. What might be up? Do I need it checking out? Thanks.

 

[Timmy D]

The filling loop could have been left open slightly and you mains pressure at the filling location could be 2 bar. This, no more pressure to increase system pressure and no noise of flowing water.

Close both filling loop valves and disconnect hose. Get bucket and open filling loop into bucket to prove mains connection.