A.O. Smith 28 30 50 60 Water temperature protection, Gas control, 3 Fan, Pressure switch

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Protection for the appliance

2.4.1	Water temperature protection
	With temperature sensor T1 g and temperature sensor T2 m, the
	ThermoControl monitors three temperatures which are important for safety.
	Table 2.1 explains the functioning of the temperature sensors.
Table 2.1 Temperature protection
Protection	Description
Against frost	The frost protection cuts in. The water is heated to 20°C.
(T1 < 5°C or T2 < 5°C)
For maximum water temperature	The high-limit safeguard serves to prevent overheating and/or excessive
(T1 > 85°C or T2 > 85°C)	formation of scale in the appliance. Should the high-limit safeguard be
	activated, the heating is halted. This causes the water in the tank to cool down.
	Once the water has cooled sufficiently (T1 < 78 °C), the ThermoControl resets
	the appliance.
For extra safety	A lockout error of the water heater controller takes place. The controller must
(T1 > 93°C or T2 > 93°C)	be manually reset before the appliance can resume operation (see paragraph
	’6.3 Error conditions’). The reset may only be performed once T1 < 78°C.

2.4.2Gas control

The ThermoControl opens the gas control so that gas can be supplied to the burner. As a safety measure, the gas control has two valves. Both valves shut off the gas supply.

Smooth ignition is achieved by opening the gas control with a delay (‘softlite’).

2.4.3Fan

The fan provides an optimum air supply when there is a heat demand. A safety aspect is that the fan ensures that any gases present in the combustion chamber get removed, both before and after combustion. We refer to this as pre- and post-purge.

The fan speed is continuously monitored by the ThermoControl. The ThermoControl takes control if the speed of rotation varies too much from the value set.

2.4.4Pressure switch

The pressure switch ensures the discharge of flue gases and the supply of incoming air during the pre-purge and normal running of the appliance. The standard position of the pressure switch is open. When sufficient pressure differential is reached, the pressure switch closes. However, in the event of a fault, the pressure switch will be tripped open, and the heating cycle will be interrupted.

Release R.1.3 UK 15