BAXI boiler hot water issues

[Henbane]

I have a BAXI combi boiler in my kitchen… the hot water works perfectly in the kitchen sink. In my bathroom, the shower also works fine after taking a while to warm up but the sink tap runs cold very quickly. It didn’t always do this, it was intermittent at first… the tap started dripping as the problem got worse but I’m not sure if this is connected. Do you know what the problem could be? Thanks