No water from hot taps?

Yesterday my husband turned off water mains, drained cold water system in order to remove a faulty shower unit. Capped the shower pipe off to prevent water coming out of that pipe (until we replace the shower) then put water back on at the stopcock. Now we have cold water from taps but no hot water. Tanks in loft have been checked, have water going into hot water tank in aring cupboard but no water between this tank and the hot taps. Please can you advise? Thank you.