Rheem Tankless Water Heater User Manual

For safe operation of the water heater, be 
sure that:

●

The pressure rating of the relief valve 
must not exceed 150 psi (1034 kPa), the
maximum working pressure of the water
heater as marked on the rating plate.

●

The BTUH rating of the relief valve must
equal or exceed the BTUH input of the
water heater as marked on its rating plate.

●

No valve of any type should be installed
between the relief valve and the water
heater

●

Discharge from the relief valve should be
piped to a suitable drain to eliminate
potential water damage. Piping used should
be of a type approved for the distribution of
hot water.

●

Hot and cold water lines should be
insulated up to the water heater. Refer 
to page 24 for details.

●

The discharge line must be NO
SMALLER than the outlet of the relief
valve and must pitch downward to allow
complete drainage (by gravity) of the
relief valve and discharge line.

●

The end of the discharge line should not 
be threaded or concealed and should be
protected from freezing. No valve of any
type, restriction or reducer coupling should
be installed in the discharge line.

Notice: Local codes govern the installation 
of relief valves. If local codes require that a
temperature and pressure relief valve should
be installed, the manufacturer recommends a
type 40XL Watts T&P relief valve or an
equivalent model be used.

Notice: Manual operation of relief valves
should be performed at least once a year. Turn
off the electrical power and gas shutoff valve.
Lift and release lever on the relief valve and
check the manual operation of the relief valve.
You should take precaution to avoid contact
with the hot water coming out of the relief
valve and to prevent water damage.

Notice: If the relief valve on the system
discharges periodically, a problem exists and
service to the water system is required.

The vinyl tubing as shown is supplied only
with indoor water heaters and connects to the
drain valve located at the hot water outlet as
shown in the diagram at left. Route the other
end of the vinyl tubing to the drain pan or a
suitable drain where leakage from the heater
will not result in damage to the area adjacent
to the heater or to lower floors of the structure.

Relief 

Valve 

Pressure
Relief
Valve

Discharge 

Water 

Shutoff 

Drain

Valve

Valve 

Hot Water 

Supply 

Union 

Outlet 

Drain 

Tube to 

suitable 

drain 

Cold 

Water 
Supply 

Inlet 

Line 

Notice: The above illustrates a
pressure-only relief valve. If local
codes require a combination
temperature and pressure relief
valve be installed, an extension
piece may be needed to ensure that
the valve probe is not directly in
the flow path of the water. 

18

Drain Valve

shown on 

right without

tubing (barb

fitting on

indoor models

only)

(indoor
models

only)