Please help! We have been away from home for a couple of months and came home to no hot water in one of the showers. Hot water fine in bathroom sinks but none in kitchen sink. Other shower plenty of hot water. I read that it is possibly the mixer valve in the shower but don't know what's wrong in kitchen?

Try this. Shut the water off and pull the cartridge, Check the inlet ports for trash and clean. Now place a pan over the open valve and turn the water back on for a minute to flush out the supply. You should have a strong stream when doing so. Reassemble and test. If that works do it on all affected taps, good luck, Tom