COMBI A - Instruction Manual

16. Sequence of

16. Sequence of operation 16.1 Central Heating Mode Activation of the time clock and/or room thermostat starts the boiler. The display panel indicates the flow temperatures in central heating as illustrated below: With the boiler in rest, the diverter valve is in the domestic hot water position, activation of the central heating changes the position of the motorised valve head, moving the diverter valve into the central heating position. The start of the pump is delayed for 7 seconds to allow the movement of the diverter valve. The PCB checks the pressure of the primary circuit, if the pressure measured is 0.8 bar or lower, the boiler will lockout after 40 seconds. The error code E02 will appear on the LCD and the pump will stop. If the pressure measured is above 0.8 bar, the boiler ignition sequence will begin. Central heating mode ON Room thermostat contact ON At first, the fan starts and the speed increases to the required ignition speed (3460 rpm), once this speed has been achieved, the safety coil of the gas valve is supplied with 230V DC, after 8 seconds the boiler checks that the burner has lit, if the boiler does not sense that the burner has lit, the error code E04 will appear on the display, should this error occur, the boiler will attempt to relight two more times (20 seconds between each attempt). After this, should the boiler still not sense a flame, error code A03 will appear on the LCD. Should the boiler detect that the burner has lit, the boiler continues to regulate as follows. The NTC fitted on the outlet of the primary circuit exchanger is the only NTC to adjust the heat output of the boiler according to the adjustable setting point. This point is adjustable from 25°C to 85°C by the user. This NTC relays information to the PCB, which in turn modulates the burner by adjusting the speed of the fan. When the NTC senses that the set temperature has been achieved (+ 4°C to the temperature set by the user), the burner will go out. To avoid excessive burner lighting, an anti-cycle timer can be set between 0 to 7 minutes in menu 4 line 48 (see Section 17 Adjustments and Settings). The speed of the pump can be set at two levels. The PCB controls the speed of the circulation pump depending on the speed set in menu 4 line 41. Setting 410 will cause the pump to operate continually at high speed, and setting 411 will cause the pump to modulate between high and low speed depending on the ∆T between the inlet and the outlet. If the ∆T is greater than 20°C the pump will run on high speed and if the ∆T is less than 20°C the pump will run on low speed. NOTE: THE DEFAULT SETTING FOR THE PUMP IS HIGH SPEED. 34

16. Sequence of operation 16.2 Domestic Hot Water Mode The Domestic Hot Water (DHW) production always has priority over the Central Heating (CH) mode. When a hot tap is turned on, the DHW flow switch is activated. The minimum DHW flow rate is 2 l/min. If the diverter valve is in the CH position it will motor into the DHW position and the boiler will start. The LCD will show that the boiler is working in hot water mode as below: The appliance follows the same operating logic as described in Section 16.1 Central Heating Mode. In domestic hot water mode NTC1 limits the maximum temperature of the primary heating circuit to 78°C during DHW production, re-ignition will occur at 74°C. The domestic hot water temperature is limited to 64°C, re-ignition will occur at 62°C. The NTC at the end of the plate heat exchanger is the only NTC used for the regulation according to the DHW setting. The DHW setting is adjustable from 40°C to 60°C by the user. The PCB compares the values of the DHW NTC with the setting of the DHW control knob. If the temperature of the DHW NTC is 4°C greater than the temperature set on the DHW control knob, the burner will go off, it will restart when the temperature of the DHW NTC is less than + 2°C of the temperature set on the DHW control knob. 35