This faucet is located in the beauty salon of a nursing home. The problem is... all of a sudden there is no hot water coming out of the faucet.

Things that have been tried...

The cold water line was shut off to the faucet and the faucet was turned on... so that it was only pulling from the hot water line, and still only cold water. Occasionally some lukewarm water comes through with this scenario. The hot water line was then disconnected from the sink and that water coming directly out of the pipe was still cold, occasionally warm. Where do we go from here? All other sinks/showers in the nursing home have hot water.