On Mon, 18 Feb 2008 14:30:12 -0800 (PST), "
wrote:

use clamp on amp meter check current draw of both heaters after
drawing a lot of water, both should match

Two people have recommended that, but neither mentioned the difficulty
of using one, iiuc.

Don't you have to separate the two power leads to use a clamp-on, so
that it goes around only one of them? Otherwise don't the current in
each of the two wires going opposite directions cancel each other out?

You could open the top and pull out one of the wires. Is that what is
intended?