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Water Connections; Thermal Expansion - GE AP12170-4 Use And Care Manual

Single and double element models side or top water connections residential 20–52 gallon
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Installing the water heater.
NOTICE: Do not apply heat
to the HOT or COLD water
connections. If sweat
connections are used,
sweat tubing to adapter
before fitting adapter to the
water connections on
heater. Any heat applied to
the water supply fittings
will permanently damage
the dip tube.

Thermal Expansion

Determine if a check valve exists in
the inlet water line. 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 softerner. 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
Water Supply Connections
Refer to the illustration below for suggested typical installation. The installation of
unions or flexible copper connectors is recommended on the hot and cold water
connections so that the water heater may be easily disconnected for servicing if
necessary. The HOT and COLD water connections are clearly marked and are 3/4" NPT on
all models. Install a shut-off valve in the cold water line near the water heater.
Typical Side Connect Installation
Electrical junction box
(use only copper conductors)
Temperature & pressure relief
Hot water outlet to fixtures
To cold water supply
Relief valve
discharge line.
Directed to under
side of home.
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 problem.
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. 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 addition
information regarding this subject.
To electrical
distribution panel
Jacket access
Shut-off valve
Jacket access
Drain valve
Auxiliary catch pan

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