Hot water only coming out of one tap

We have a gas heating boiler that also heats our tap water but ever since we've had the water turned off to fit a shower, the hot water only comes out of the bathroom now and not the kitchen.

The boiler is in the kitchen so it's closer to the tap that isn't working but when turned, we only get drops but there's full flow in the bathroom.

Any ideas what it might be or what I could do?

It's a nightmare having to boil the kettle 2-3 times every time I was the dishes.