Installing the water heater.
Determine if a check valve exists in the
inlet water line. Check with your local
water utility. It may have been installed
in the cold water line as a separate back
flow preventer, or it may be part of a
pressure reducing valve, water meter or
water softener. A check valve located
in the cold water inlet line can cause
what is referred to as a “closed water
system”. A cold water inlet line with
no check valve or back flow prevention
device is referred to as an “open” water
As water is heated, it expands in
volume and creates an increase in
the pressure within the water system.
This action is referred to as “thermal
expansion”. In an “open” water
system, expanding water which exceeds
the capacity of the water heater flows
back into the city main where the
pressure is easily dissipated.
A “closed water system”, however,
prevents the expanding water from
flowing back into the main supply line,
and the result of “thermal expansion”
can create a rapid and dangerous
pressure increase in the water heater
and system piping. This rapid pressure
increase can quickly reach the safety
setting of the relief valve, causing it
to operate during each heating cycle.
Thermal expansion, and the resulting
rapid and repeated expansion and
contraction of components in the water
heater and piping system can cause
premature failure of the relief valve,
and possibly the heater itself. Replacing
the relief valve will not correct the
The suggested method of controlling
thermal expansion is to install an
expansion tank in the cold water line
between the water heater and the
check valve (refer to the illustration
on page 9). The expansion tank is
designed with an air cushion built in
that compresses as the system pressure
increases, thereby relieving the over
pressure condition and eliminating the
repeated operation of the relief valve.
Other methods of controlling thermal
expansion are also available. Contact
your installing contractor, water supplier
or plumbing inspector for additional
information regarding this subject.
Inspect Water Heater
Inspect the water heater for possible damage. Check the markings on the rating
plate of the water heater to be certain the power supply corresponds to the water
Vacuum Relief Valve
NOTICE: DO NOT operate
the unit without the vacuum
relief valve for any reason.
Doing so will void the
The vacuum relief valve, which must
be used when installing the water
heater, is factory installed.
The cold water inlet has a vacuum
relief valve connected to it. Certain
conditions in the field may produce a
vacuum or negative pressure condition
inside the water heater’s tank. This
negative pressure can cause the tank to
fail. The vacuum relief valve provides
a means to eliminate the negative pres-
sure or vacuum by admitting air into
the tank to equalize the pressure.
It is not recommended to pull a
vacuum on the unit.
If a vacuum is pulled on the unit, refer
to the "To Fill the Water Heater" sec-
tion to ensure the unit is full of water