A.O. Smith SGE Flame probe, Safety of the installation, Unvented installation, 3 T&P valve

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2.4.6Flame probe

To ensure that no gas can flow when there is no combustion, the water heater is fitted with a flame probe (21). The electronic controller uses this probe to detect the presence of a flame, by means of ionisation detection. The electronic controller closes the gas control the instant it detects that there is a gas flow but no flame.

2.5Safety of the installation

In addition to the appliance's standard built-in safety monitoring, the appliance must also be protected by an expansion vessel, expansion valve, pressure reducing valve, non-return valve and a T&P valve.

The use of an expansion vessel, expansion valve and/or pressure reducing valve depends on the type of installation: unvented or vented.

2.5.1Unvented installation

With an unvented installation, an expansion valve valve and expansion vessel prevent the buildup of excessive pressure in the tank. This prevents damage being caused to the enamelled coating (in the appliance) or to the tank. A non- return valve prevents excessive pressure buildup 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 installation against an excessively high water supply pressure (> 8 bar). These components are fitted to the cold water pipe (3.7 "Water connections, Vented").

2.5.2Vented installation

With a vented installation, excess pressure is taken up by the open cold water head tank. The height of the head tank determines the working pressure in the water heater, which may not exceed 8 bar. The installation must also be fitted with a vent pipe from the hot water pipe, that opens into the cold water tank.

Ideally, the vent pipe should discharge into a separate tundish/drain or otherwise to the open cold water head tank. The water heater should also be fitted on the hot water side with a stop valve (3.6.2 "Hot water side").

2.5.3T&P valve

A T&P valve is only mandatory in an unvented installation. 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 excessive (> 10 bar) or the water temperature is too high (> 97°C), the valve will open. The hot water can now flow out of the tank. Because the appliance 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 appliance is fitted standard with a connecting point for a T&P

valve (3.6.2 "Hot water side").

2.6Protection for the solar heating system

2.6.1Drain-back tank

The solar heating system may optionally be equipped with a drain-back tank. The tank fills itself with the heating fluid when there is no heat demand. This avoids overheating of the solar heating system. The high insulation factor of the tank also protects the system from freezing of the fluid. The use of the drain- back tank also serves to extend the useful life of the fluid.

The presence of a drain-back tank is set (12.9.1 "Setting the drain-back tank") during the installation. Refer to the solar heating system manual for more details.

Instruction manual SGE 17