A.O. Smith GWV - 120, Installation And Service Manual

Page: 16 / 102

Working principle of the appliance
16 Instruction manual GWV
2
gis
2.4 Protection for the
appliance
2.4.1 Introduction
The electronic controller monitors the water temperature and ensures safe
combustion. This is achieved by:
•
the Water temperature protection
• the Gas control
• the Fan
• the Pressure switch
• the Flame probe
• the Flow-through switch
2.4.2 Water temperature protection
The electronic controller monitors the water temperature with temperature
sensors T
1
, T
2
and T
3
as shown in the table.
Temperature protection
2.4.3 Gas control
When heat is required, the controller (5) opens the left-hand gas control (9) so
that the gas can flow into the premix bar burners (18) of the first tray of burners.
The air is mixed in with the gas at the front of the burners. The hot surface igniter
(17) ignites the leftmost burner. The adjacent burners then ignite from left to
right.
If more heat is demanded, the controller opens the second gas control (9) as
well. There is no separate igniter for the ignition of the second tray of burners.
The gas controls have two valves as safety devices. The valves shut off the gas
supply.
Smooth ignition is achieved by opening the gas controls with a delay ("softlite").
2.4.4 Fan
The fan (10) provides an optimum air supply (8) when there is a heat demand.
This air comes into a separate chamber on the air distribution plate (13).
Overpressure is created in the space and the air can only escape the appliance
via the premix bar burners (18).
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-purge and post-purge.
The fan speed is continuously monitored by the electronic controller (5). The
electronic controller takes control if the speed of rotation varies too much from
the set value.
2.4.5 Pressure switch
The pressure switch (12) guarantees the air supply during pre-purging and
when the appliance is operational. The standard position 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.
Safety Description
T
1
, T
2
, T
3
> 98°C The appliance switches back to partial load once the heat demand has been
met.
For additional safety
T
1
, T
2
, T
3
> 99°C
A lockout error of the appliance occurs. The controller must be manually reset
before the appliance can resume operation (8.3 "Error conditions") . The reset
may only be performed if T
3
< 90°C.