How do I turn the water off to empty a emmersion heater?

look for the pipe with the red valve (gate valve) shut that.
open your bath hot tap fully.
the water will stop in a matter of seconds.

now slacken the element enough to have made it fee not not leak water.

now follow that pipe with the gate valve on to the bottom of your tank there should be a drain cock fitted just before it enters the bottom of tank.
fix a hose and then undo your draincock enough to drain the water.
drain for about five mins then unscrew your element if it don't start seeping water you have gone low enough to remove it.

shut draincock change element, shut bath tap, open gate valve, allow to fill then check your hot taps to make sure you don't have any airlocks.

hi-spec plumbing
August 2007