A.O. Smith SGE Appliance water temperature protection, Gas valve, 4 Fan, Pressure switch

2

2.4.2

Working principle of the appliance gis

Appliance water temperature protection

	The electronic controller (4) controls and monitors the safety of the appliance by
	means of sensors T1 and T2 . S2 is also used for protection of the appliance.
	However, this is primarily intended for control of the solar heating
	system (2.6 "Protection for the solar heating system").
	The table explains the functioning of these temperature sensors.
	Temperature protection
Protection	Description
Against frost:	The frost protection cuts in. The water is heated to 20°C.
- T1 < 5°C
- T2 < 5°C
For maximum water temperature:	The high-limit safeguard serves to prevent overheating and/or excessive
- T1 > 85°C	formation of scale in the appliance. If the high-limit safeguard is activated, the
- T2 > 85°C	heating is stopped. This causes the water in the tank to cool down. Once the
- S2 > 85°C	water has cooled sufficiently (T1 < 78°C), the electronic controller resets the
	appliance.
For extra safety:	A lockout error of the water heater controller takes place. The controller must
- T1 > 93°C	be manually reset before the appliance can resume operation (8.3 "Error
- T2 > 93°C	conditions"). The reset may only be performed if T1 <78°C.
- S2 > 93°C

2.4.3Gas valve

The electronic controller opens the gas valve so that gas can be supplied to the burner. As a safety measure, the gas valve has a double shut-off. The double shut-off guarantees complete isolation of the appliance from the gas supply.

To help ensure smooth ignition, the gas valve opens gradually ('softlite").

2.4.4Fan

The fan (18) provides an optimum air supply when there is a heat demand. As a safety feature, the fan ensures that any gases present in the combustion chamber are removed, both before and after combustion. We refer to this as pre- and post-purge.

The fan speed is continuously monitored by the electronic controller (4). The electronic controller takes control if the speed of rotation varies too much from the set value.

2.4.5Pressure 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 default state of the pressure switch is open. When sufficient pressure difference is reached, the pressure switch closes. However, in the event of a fault, the pressure switch is tripped open, and the heating cycle is interrupted. The table shows the trip point per appliance.

Note

The trip point of the pressure switch is not adjustable.

Pressure switch trip points

Appliance	Closing pressure	Opening pressure
	difference	difference
SGE 40
SGE 60	> 675 Pa	< 645 Pa

16 Instruction manual SGE