Safety Of The Installation - A.O. Smith SGS-28 Installation, User And Service Manual

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6.3.1.6
6.3.2
6.3.2.1
6.3.2.2
6.3.2.3
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closes. Refer to the general and electric specifications in the appendices (see section 12)
for the trip point for each water heater.
Note
The trip point of the pressure switch is not adjustable.
Flame probe
To ensure that no gas can flow when there is no combustion, the water heater is fitted
with a flame probe (21). The controller uses this probe to detect the presence of a flame,
by means of ionisation detection. The controller closes the gas control valve the instant it
detects that there is a gas flow but no flame.

Safety of the installation

Excessive pressure in the tank can damage the enamelled layer (in the water heater) or
the tank itself. An inlet combination and pressure-reducing valve prevents this. The inlet
combination acts as a stop valve, non-return valve and overflow valve. If the water mains
pressure is too high, a pressure-reducing valve must be used (Refer to the general and
electric specifications in the appendices (see section 12)). Both components must be fitted
in the cold water inlet (see section 7.4.2).
The use of an expansion vessel, expansion valve and/or pressure reducing valve depends
on the type of installation: unvented or vented.
Unvented installation
With an unvented installation, an expansion valve and expansion vessel prevent the
buildup of excessive pressure in the tank. This prevents damage being caused to the
enamel coating (in the water heater) or to the tank. A non-return valve prevents excessive
pressure build-up in the water supply system. This valve also prevents water from flowing
backwards from the tank into the cold water supply system. The pressure-reducing valve
protects the water heater against excess mains water pressure, refer to the general and
electric specifications in the appendices (see section 12). These components are installed
in the cold water inlet (see section 7.4.2).
Vented installation
With a vented installation, excess pressure is taken up by the open cold water head tank.
The level of the cold water head tank determines the maximum working pressure in the
tank, refer to the general and electric specifications in the appendices (see section 12).
The water heater must also be fitted with a vent pipe from the hot water pipe, which
opens into the cold water head tank.
Ideally, the vent pipe should discharge into a separate discharge channel/drain or
otherwise to the open cold water head tank. The water heater should also be fitted with a
stop valve (see section 7.4.1.2) on the hot water side.
T&P valve
A T&P valve is only mandatory in unvented installations. However, A.O. Smith also
recommends the use of a T&P valve in vented installations.
A T&P (Temperature and Pressure Relief) valve monitors the pressure in the tank and the
water temperature at the top of the tank. If the pressure in the tank becomes too high the
valve will open, refer to the general and electric specifications in the appendices (see
section 12). The hot water can now flow out of the tank. Because the water heater is
under water supply pressure, cold water will automatically flow into the tank. The valve
remains open until the unsafe situation has been rectified. The water heater is fitted
standard with a connection for a T&P valve (see section 7.4.1.2).
Installation, Maintenance and Service part