Hi, the hot tap on the bathroom basin has suddenly packed up. It has to be turned full on to get any water, and then just a trickle. All other hot taps are fine, including others upstairs. We recently had a new combi boiler installed if that is relevant. The tap that's not working is about ten years old. I would like to try and repair it myself but haven't a clue where to start so any help would be much appreciated. many thanks.