Tip to save calling a plumber.

Just got to tell you this!  If you get air in your hot water system the flow could be reduced and noisy, gurgles etc. and spluterings at the tap.
     Go to your washing machine and swap the hot and cold pipes over , turn water back on for a minute . High pressure cold water forces hot water (and air) back into tank and problem cured.
  Alternative is , if possible , connect hot and cold taps in kitchen with short bit of hose and turn both taps on for a minute. Simplest way if you have a round section mixer tap with a unscrewable end cap with holes in is to unscrew it and put two layers of cooking foil in and screw it back on. this blocks the water, then turn on hot tap then cold for one minute and no more trouble!