A.O. Smith SGE service manual Starting and running, Icon is activated Message PRE Purge appears

9 Starting and running

The complete cycle is explained in the following example, which assumes the appliance is in the basic mode ON.

Note

The same heating cycle applies to the other operating modes.

Once the appliance starts, it will run through the following steps:

1.The water temperature drops below the set temperature of (for example) 65°C. The electronic controller detects a demand and starts the heating cycle.

-The icon is activated.

-The message HEAT DEMAND appears.

a

ON Ê

13:45 Thursday 63ÉC

Tset 65ÉC

HEAT DEMAND

2.Once demand is registered, the fan is started to exhaust any gases that may be present. This phase is called pre-purge and lasts about 15 seconds.

-The icon is activated.

-The message PRE PURGE appears.

a

ON Ê Ê

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Tset 65ÉC

PRE PURGE

3.During the pre-purge, the pressure switch closes.

-The icon is activated.

-The message PRESSURE SWITCH appears.

a

ON	Ê Ê Ê
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	Tset 65ÉC
PRESSURE	SWITCH

4.After some time, the pre-purge ceases and the electronic controller reduces the fan speed to the ignition speed. This is followed by the (pre-)glow of the hot surface igniter.

-The icons and are dimmed

-The icon is activated.

a

ON	Ê	Ê
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	Tset 65ÉC
GLOW PLUG

gis

5.After a number of seconds pre-glow, the gas control is opened and ignition takes place.

-The icon is activated.

-The message IGNITION appears.

a

ON	Ê	Ê Ê
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	Tset 65ÉC
IGNITION

6.After ignition, the flame is detected and the appliance will be running. This means that actual heating has started. The fan speed then increases to the normal working speed, and the pressure switch closes:

-The icon is dimmed.

-The icons and are activated.

-The message RUNNING appears.

a

ON	Ê Ê	Ê Ê
13:45 Thursday		63ÉC
	Tset 65ÉC
RUNNING

7.When the water is up to temperature, the heat demand drops off and the post-purge starts. This lasts about 25 seconds.

-The icons , and are dimmed.

-The icon is activated.

-The message POST PURGE appears.

a

ON	Ê Ê
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	Tset 65ÉC
POST PURGE

8.Following the post-purge, the fan stops and the pressure switch opens:

-The icons and are dimmed.

-The message POST PURGE vanishes.

a

ON

14:05 Thursday 65ÉC

With any subsequent heat demand, the heating cycle will resume from step 1.

62 Instruction manual SGE