I have a Combi toilet with basin on top, I fitted it in 2019 and everything was fine until earlier this month when the feed to the basin stopped. The cold feed to the toilet which is a T off from the basin supply is still running. I’ve turned both the hot and cold off and turned them back on but this didn’t change anything. I didn’t want to pull it all apart if I can help it as it is a confined space. I checked the cassette/cartridge in the tap for limescale build up but it was clean. We are in a soft water area. Can you suggest a fix ?