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9
Safety Instructions Installation Instructions Operating Instructions Care and Cleaning Troubleshooting Tips Customer Service
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 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 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 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 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 (see illustration below). 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.
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
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
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.
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.
WARNING: The water heater should not be installed in a space where liquids which give off flammable vapors
are to be used or stored.
Shut-off valve
Thermal expansion
tank (if required)
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