if it's both the hot and cold i'm inclined to believe there is junk stuck where the two water channels come together and enter the spout.does it have a sprayer?maybe the diverter got stuck partally.take spout off see if you can blow air through it easily cover opening with a cup turn water on to flush it out,try removing diverter,put back together less the diverter,see if there is any difference.is it a single handle model or 2 handle?let us know how you made out.