A.O. Smith SGS - 100, Installation & Service Manual

Page: 16 / 110

Working principle of the appliance
16 Instruction manual SGS
2
gis
2.4.2 Appliance water temperature protection
The electronic controller uses temperature sensors T
1
(7) and T
2
to monitor
several temperatures that are important for safety.
The table explains the functioning of these temperature sensors.
Temperature protection
2.4.3 Water temperature protection for the storage tank
Using temperature sensors S
2
and S
3
, the solar heating system controller
monitors several temperatures in the storage tank that are related to safety.
Temperature protection
2.4.4 Gas 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").
2.4.5 Fan
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.
Protection Description
Against frost:
- T
1
< 5°C
- T
2
< 5°C
The frost protection cuts in. The water is heated to 20°C.
For maximum water temperature:
- T
1
> 85°C
- T
2
> 85°C
The high-limit safeguard serves to prevent overheating and/or excessive
formation of scale in the appliance. If the high-limit safeguard is activated, the
heating is stopped. This causes the water in the tank to cool down. Once the
water has cooled sufficiently (T
1
< 78°C), the electronic controller resets the
appliance.
For extra safety:
- T
1
> 93°C
- T
2
> 93°C
A lockout error of the water heater controller takes place. The controller must
be manually reset before the appliance can resume operation (8.4 "Error
conditions") . The reset may only be performed if T
1
<78°C.
Protection Description
Against frost:
- S
2
, S
3
< 5°C
The frost protection cuts in. The water is heated to 20°C.
For maximum water temperature:
- S
2
, S
3
> 85°C
The high-limit safeguard serves to prevent overheating and/or excessive
formation of scale in the storage tank. If the high-limit safeguard is activated,
the heating is stopped. This causes the water in the storage tank to cool down.
Once the water has cooled sufficiently (S
3
< 78°C), the electronic controller
resets the appliance.
For extra safety:
- S
2
, S
3
> 93°C
A lockout error of the water heater controller takes place. The controller must
be manually reset before the appliance can resume operation (8.4 "Error
conditions") . The reset may only be performed if S
3
< 78°C.