A.O. Smith 28 30 50 60, Installation & Service Manual

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The appliance’s heating cycle
Release R.1.3 UK 51
gis
7.4 The appliance’s
heating cycle
The appliance’s heating cycle is activated as soon as the measured water
temperature (T
net
) falls below the threshold value (T
set
). This threshold value
depends on the currently selected appliance operating mode. For example, if
the appliance is in the “OFF mode” (frost protection), then this value is 5°C. If
the appliance is in the “ON mode”, then this threshold value is selectable, for
example, 65°C.
The heating cycle runs in turn through the following states:
1. HEAT DEMAND;
2. PRE-PURGE;
3. PRESSURE SWITCH;
4. PRE-GLOW;
5. IGNITION;
6. RUNNING;
7. POST-PURGE.
The complete cycle is explained in the example set out below assuming the
appliance is operating in mode
ON
.
n Remark
The same heating cycle applies to the other operating modes.
Once the appliance starts, it will run through 8 steps:
1. The water temperature drops below the set temperature of (for example)
65°C. The ThermoControl detects a heat demand and starts the heating
cycle.
-
The
W
icon is activated.
- The message
HEAT DEMAND
appears.
2. Following the heat demand, the fan is powered up and the pre-purge begins.
This lasts about 15 seconds. During this phase, any residual gases are
removed.
-
The
S
icon is activated.
- The message
PRE PURGE
appears.
3. During the pre-purge, the pressure switch closes.
- The
D
icon is activated.
- The message PRESSURE SWITCH appears.
4. After some time, the pre-purge ceases and the ThermoControl reduces the
speed of the fan to the rotational speed for ignition. This is followed by the
pre-glow of the glow igniter.
-
The
S
and
D
icons are dimmed.
- The
O
icon is activated.
ON Ê
13:45 Thursday 63ÉC
Tset 65ÉC
HEAT DEMAND
Figure 7.8 Frost protection cuts
in
ON Ê Ê
13:45 Thursday 63ÉC
Tset 65ÉC
PRE PURGE
Figure 7.9 Pre-purge
ON Ê Ê Ê
13:45 Thursday 63ÉC
Tset 65ÉC
PRESSURE SWITCH
Figure 7.10 Pressure switch
ON Ê Ê
13:45 Thursday 63ÉC
Tset 65ÉC
GLOW PLUG
Figure 7.11 Pre-glow