Past comes back to haunt me.

[SteamyTea]

While filling the bath, the shower pump seemed starved of water.

Shut the taps, bathed, got up in loft and the cold tank is not refilling.

Shut off water, removed ballcock and valve.

The little white plastic cone that has a hole in the middle has a small screw in it.

The same screw I dropped down a pipe when changing the cylinder a few years ago.

Ten minutes, problem sorted.