Specifications
Copyright© by AOS 2015. All rights reserved.
Safety
Excessive Temperatures
The T&P valve will also acvate when the water
temperature exceeds 210°F. Acvaon of the T&P valve
for excessive temperatures will result in a large amount of
water being discharged and could indicate a problem with
the control circuit. This problem should be corrected at
once in order to prevent scalding injuries.
Gas water heaters are equipped with an energy cuto
(ECO) switch. It is designed to shut o the gas supply to
the unit if the water temperature exceeds about 190°F.
The ECO is a single use switch and requires complete
replacement of the enre thermostat if acvated.
Electric water heaters have a high limit control switch,
shown above, which will shut o power to the elements if
water temperatures exceed about 170°F. This switch can
be reset by rmly pushing the red reset buon located on
the thermostat.
When a series of short draws of hot water are used
from the tank, usually 3 gallons or less, it can arcially
increase the number and frequency of heang cycles. With
each draw, cool water enters the boom of the tank. The
lower thermostat senses a change in temperature
acvang the lower element or burner. Since a short draw
of water does not completely remove all the hot water in
the top of the tank, increasing the number of heang
cycles adds more temperature to water in the top of the
tank. This is called stacking.
Electric water heaters are not as subject to stacking as gas
water heaters because, on short draws all the heat
produced by the heang element is transferred to the
water in the boom 1/3 of the tank and mixes with the
surrounding water. For this reason, electric water heaters
usually do not stack more than about 5°F.
Gas water heaters can stack up to 30°F. Heat from the
burner is transferred through the ue at the top of the
water heater as well as through the boom head.
Repeated short draws accompanied by short heang
cycles allow the ue to overheat water in the top of the
tank without the thermostat sensing it.
Stacking increases the chance of scald injuries. A mixing
valve greatly reduces the chance of a scalding injury due to
stacking by automacally adjusng the proporon of cold
to hot water as water is drawn from the tank. In homes
where children, elderly people or the disabled are present,
a mixing valve is recommended for general use xtures.
Submerged Water Heaters
When a water heater has been submerged in water, such
as during a ood, it must be replaced. The operang
controls can no longer be considered funconally safe. The
insulaon surrounding the unit will have become
saturated and cannot be fully dried out. This will cause the
outer surface of the tank to corrode creang
potenally unsafe operang condions.