A.O. Smith BFM - 120 manual Starting and running, Starting the appliance, Appliances heating cycle

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9 Starting and running

9.1Introduction

Topics covered in this chapter:

•Starting the appliance;

•The appliance's heating cycle.

9.2Starting the appliance

Start the appliance as follows:

1. Fill the appliance (5 "Filling").

2.Open (3.5 "Installation diagram") the manual gas valve.

3.Switch on the power to the appliance using the isolator between the appliance and the power supply.

4.Put the appliance in ON mode by setting the ON/OFF-switch on the control panel to position I.

5.Using the control thermostat (7.5 "Control thermostat"), set the desired water temperature.

If there is a heat demand, the appliance will run through the heating cycle (9.3 "The appliance's heating cycle").

9.3The appliance's heating cycle

The appliance's heating cycle is activated as soon as the measured water temperature (Twater) falls below the threshold value (Tset). This threshold value depends on the currently selected appliance operating mode. For example, if the appliance is in OFF mode (frost protection), then this value is 20°C. If the appliance is in ON mode, for example, then this threshold value can be selected, e.g. position 3 (± 60°C).

The heating cycle runs successively through the following states:

1.HEAT DEMAND;

2.WAIT;

3.PRE-GLOW;

4.IGNITION;

5.RUNNING;

6.WAIT.

The entire cycle is explained in the example below.

Note

The cycle has the same steps when frost protection is activated.

1.The control thermostat sensor measures the temperature. The water temperature falls below the set temperature of (for example) 60°C, causing the control thermostat to close. The burner control now detects a demand and starts the heating cycle.

2.Following demand, the wait period starts. This wait ensures that the ignition is safe. The wait period lasts approximately 15 seconds.

3.Once the wait period has elapsed (there is audible ‘clicking’ of the relay in the burner control), the PRE-GLOW starts.

4.After about 12 seconds (pre)glowing, the gas control opens and ignition takes place.

5.After ignition, the flame is detected and the appliance will be running. This means that actual heating has started.

6.When the water reaches the set temperature, the demand ceases. The gas control closes and the burner tray is extinguished. A new wait period of about 10 seconds starts.

7.At the end of this wait, the appliance enters the idle state, and waits until the water temperature once more falls below the set temperature.

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

Instruction manual BFM 53