My mind tells me it's fed by a hot storage tank and could have developed an airlock. Sometimes it can be released turning on all the hot taps. If no go turn all hot taps off again and connect cold tap to the offending hot with a length of hose turn on both taps the cold will force the airlock back to the tank. Another but watch it
the hose connected to hot tap let residue water run out then with big strong puff blow up the pipe, I've done that and strange as it seems out gushed the water it seems the water just wanted a kick start to flow freely.
Nobby
January 2009