Water Piping General Instructions; Pressure Relief Valve; Freeze Protection - A.O. Smith 705 Operation & Installation Manual

Direct vent tankless water heater
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Water Piping
General Instructions
• A manual water control valve must be placed in the
water inlet connection to the water heater before it is
connected to the water line. Unions may be used
on both the hot and cold water lines for future
servicing and disconnection of the unit.
• The piping (including soldering materials) and
components connected to this appliance must be
approved for use in potable water systems.
• Purge the water line to remove all debris and air.
Debris will damage the water heater.

Pressure Relief Valve

• An approved pressure relief valve is required by the
American National Standard (ANSI Z21.10.3) /
Canadian Standard (CSA 4.3) for all water heating
systems.
• The relief valve must comply with the standard for
Relief Valves and Automatic Gas Shutoff Devices
for Hot Water Supply Systems ANSI Z21.22 and /or
the standard Temperature, Pressure, Temperature
and Pressure Relief Valves and Vacuum Relief
Valves, CAN1-4.4.
• The relief valve must be rated up to 150 psi and to
at least the maximum BTU/hr of the appliance.
• The discharge from the pressure relief valve should
be piped to the ground or into a drain system to
prevent exposure or possible burn hazards to
humans or other plant or animal life. Follow local
codes. Water discharged from the relief valve could
cause severe burns instantly, scalds, or death.
• The pressure relief valve must be manually
operated once a year to check for correct operation.

Freeze Protection

The freeze protection features include electrical
heating elements and intermittent firing of the burner.
Freeze protection may be disabled if electricity or gas
is not supplied, or if there is an error preventing the
water heater from functioning. Loss of freeze
protection may result in water damage from a burst
heat exchanger or water lines.
The installation of auto drain down solenoid valves is
optional. However, it is strongly recommended that
these valves be installed to prevent damage from
freezing in case the normal freeze protection should
become disabled. Any product damage due to
freezing will not be covered by the warranty.
• Toxic chemicals such as those used for boiler water
treatment are not to be introduced to the potable
water used for space heating.
• If the appliance will be used as a potable water
source, it must not be connected to a system that
was previously used with a nonpotable water
heating appliance.
• Ensure that the water filter on the water heater is
clean and installed.
• The relief valve should be added to the hot water
outlet line according to the manufacturer's
instructions. DO NOT place any other type valve or
shut off device between the relief valve and the
water heater.
• Do not plug the relief valve and do not install any
reducing fittings or other restrictions in the relief line.
The relief line should allow for complete drainage of
the valve and the line.
• If a relief valve discharges periodically, this may be
due to thermal expansion in a closed water supply
system. Contact the water supplier or local
plumbing inspector on how to correct this situation.
Do not plug the relief valve.
• Neither this water heater nor the American National
Standard (ANSI Z21.10.3) / Canadian Standard
(CSA 4.3) requires a combination temperature and
pressure relief valve for this appliance. However,
local codes may require a combination temperature
and pressure relief valve.
In addition, the solenoid valves should be connected
electrically to a sub-PC board that attaches to the PC
board in the unit. This allows the solenoid valves to
operate if the water heater is disabled due to an error
code.
The solenoid valves and sub-PC board are available
for purchase separately.
305, 505, 705 Indoor Manual
17

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