In addition to following adjustment the Blower Fan Adjustment also applies.
The Semi Automatic Boilers are equipped with controller and a fan which operates until the boiler reaches the set temperature.
Once set temperature is reached the boiler controller proceeds to its sustain mode.
Following a period of several minutes of idling the boiler will automatically activate the air fan to blow through any gases and sustain a flame. This process occurs in repeating intervals until the boiler water temperature drops and controller activates the fan full time. The blow through time is around 10 seconds. Adjustments of breaks too short between the blow through will result in water temperature reaching higher than set level in the boiler.
Ideally the blow through time should be set between 20-45 mins, this should be established when monitoring the boiler temperature and is a guide line only as parameters vary and are based on individual plumbing installations.
Hysteresis settings in the semi automatic boiler, controls the oscillation limits of boiler temperature.
Graph below shows boiler temperature being set at around 65C and hysteresis at 3-4C.
The drop in internal boiler temperature below the set temperature level minus hysteresis results in the repeated activation of the fan and process of building up the temperature starts again.
The boiler computer also control the operation of the CH (central heating main) pump and the DHW (CHW - Domestic Hot Water) pump.
If your plumbing system consists only of flow and return pipe at the boiler, ignore and isolate cable labelled CHW Pump and ignore CHW Sensor.
Adjusting the fan speed and thus oxygen is essential for proper combustion. With fan speed set too low this will give poor combustion and the boiler will fail to achieve temperature level suitable to heat the water in the installation. Setting the fan speed to too high will burn the fuel too fast with loss of energy and heat escaping to the atmosphere through the chimney.
Most of our boilers are equipped with intelligent controllers, these eliminate the need for manual fan adjustment. Once boiler temperature is set, the burner becomes automated.
Manually fed boilers should be switched off when refuelling to avoid flames or smoke escaping in to the room when fan cycle goes in to blow mode.