I have a radiant floor heating application. It will contain an
Electric Hot Water Heater. This heater will NOT have a continuous
water source connected to it. Instead, the system will be a "Closed"
system. The water or anti-freeze will fill the Hot Water Heater, as
well as the tubes that go through the flooring. The fluid will return
back through the hot water heater in a Closed system.

I was told that if I get a leak in the system, I am in danger of a fire
hazard, since no fluid will be passing through the hot water heater
which has a heating element that will likely catch fire and create a
larger hazard.

I am looking for a way to sense when fluid stops passing back into the
hot water heater, and when this condition is true, I want to be able to
shut off the electricity supply to the Hot Water heater, to eliminate
my fire hazard.

Any ideas about what I should be seaching for?