Rheem XP50T06PV42U0 Instruction Manual download pdf (Page 9)

Thermal Expansion

Determine if a check valve exists in the

inlet water line. Check with your local

water utility company. 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.

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.

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

and heat traps.

NOTICE: The

National Fuel Gas

Code (NFGC)

mandates a manual

gas shut-off valve:

See (NFGC) for

complete instructions.

Local codes or

plumbing authority

requirements

may vary from

the instructions

or diagrams

provided and take

precedent over these

instructions.

Heat trap

6” minimum

Heat trap

6” minimum

Union

To gas supply

Sediment trap

Cap

Ground joint union

Drain Pan Pipe

to suitable drain.

Drain

valve

Relief valve discharge

line to suitable open

drain.

To cold water

supply

6” Air gap

Blower assembly

1/4” per foot maximum slope up or

down for horizontal venting.

Auxiliary catch pan

Union

Anode

Vent connector

Thermostatic gas valve

Jacket door

Manual gas shut-off

Temperature and pressure

relief valve

Shut-off valve

Shut-off

valve

Thermal expansion

tank (if required)

Combustion Air

Inlet Openings

Hot water outlet to

fixtures

Water Heater Jacket

Flammable Vapor Sensor

Typical Installation

Remote Control

Transformer Box

(Remote Control Models Only)

(Factory Installed Option)

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Rheem XP50T06PV42U0 Instruction Manual Page 9

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