Have had this in our Kitchen for about 4 years. This morning when I turned it on to hot the water pressure drops and can't get hot water to work. The cold water is fine. Any suggestions on what could be wrong and how to fit it?

Sounds like the Cartridge is bad, open the link below and see The Interactive Parts Diagram, you need to replace P/N GP1017426, Thanks.

John

Kohler Plumbing (http://www.kohlerserviceparts.kohler.com/ServicePartsPage.aspx?DocumentID=4158f284209642a99 4f2a18ea436fd8f&ModelID=8bb94b2b965642738b4aebe27d2730f7)

Or your water supply is kinked, angle stop clogged or water supply connector filled with debris. Close angle stop, clean water connector, make sure you don't kink it - and reinstall. See if that helped. Back to you. Milo