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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 system”.
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
dissapated.
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 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
additional information regarding this subject.
9
Safety Instructions Installation Instructions Operating Instructions Care and Cleaning Troubleshooting Tips Customer Service
Thermal Expansion
Water Supply Connections
IMPORTANT: 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
cold water connections on
heater. Any heat applied to
the cold water supply
fittings will permanently
damage the dip tube.
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 Installation
R
E
L
I
E
F
V
A
L
V
E
COLD
HOT
Heat trap
6″ minimum
Heat trap
6″ minimum
Union
Hot water outlet
to fixtures
Temperature and
pressure relief valve
Relief valve
discharge line to
suitable open drain.
To gas supply
Water Heater Jacket
Sediment trap
Cap
Jacket door
Auxiliary catch pan
Ground joint union
Drain
valve
To cold water
supply
6″ air gap
Shut-off
valve
Draft hood
Pitch up 1/4″
per foot
Union
Thermostatic gas valve
Anode
Vent connector
to chimney
Manual gas shut-off
5 feet
from the
ground
minimum
Shut-off valve
Thermal expansion
tank (if required)