Turning Off Hot Water To Fix a Tap ~ Combi

[severen]

Hi all,
noob help please.
got a Baxi 105HE, what do i need to do to turn of the water for my bath mixer tap? there's a valve under the kitchen sink, i'm presuming that's only for the cold supply? Do i just turn off the combi water or do i need to shut the power off too?

TIA

 

[flameport]

The cold supply also supplies the boiler, so turning that off should do both hot and cold.