Boiler On switch in on position/Preheat switch on/winter switch on

Central Heating mode
When the internal/external controls (i.e. programmer/room stat etc) are calling for heat the display will show ‘C’ and the ignition sequence will commence.

Once the boiler has ignited the burner ‘on’ neon on the display will be illuminated, the diverter valve will be in the central heating position.

The boiler will run at maximum until the water temperature (inside the boiler) reaches 3 deg C below the Central heating thermistor set point (RHS knob – range between 30 – 82 deg C) then it will continue to run at a modulated rate until the temperature rises 2 deg C above the temperature set point. (The ‘C’ remains on display and the burner ’on’ neon will flash). The boiler will re ignite when he temperature drops 5 deg C below the set temperature.

When the system controls are switched off the burner on neon will go out and the ‘C’ will be displayed for approximately 5 minutes to indicate pump overrun mode. (To circulate the excess heat from the boiler). The boiler display will then change to ‘O’.

Domestic hot water
When a hot tap is turned on the thermistor in the plate heat exchanger senses a drop in temperature as the cold water passing across it. The boiler will display a ‘d’ and the ignition sequence will commence.

Once the boiler has ignited the burner ‘on’  neon on the display will be illuminated and the diverter valve will be in the Domestic hot water position.

The boiler will continue to fire to maintain the domestic hot water temperature as set by the domestic hot water thermistor (RHS knob – range between 42- 65 deg C) unless the temperature exceeds the maximum domestic hot water temperature for more than 1 minute at which point the burner will go off, neon will flash until the temperature has dropped sufficiently to allow boiler to re ignite.

When the tap is turned off the boiler will continue to run until the thermistor inside the plate heat exchanger senses a rapid rise in temperature. When this occurs the burner ‘on’ neon will go out and the ‘d’ will be displayed for 5 seconds to indicate pump overrun, then the boiler will revert to ‘O’ or ‘C’ if controls are calling for central heating.

Preheat
If the thermistor inside the plate heat exchanger senses the temperature has dropped below 35 deg C the boiler will display ‘t’ and the ignition sequence will commence. The boiler will operate for approximately 2 minutes to increase the temperature in the plate heat exchanger to 65 deg C, the display will then change to ‘O’.
This function will operate approximately every 1.5 – 2hrs
Pre Heat switch off
If the preheat switch is in the ‘off’ position the boiler will not preheat as the thermistor in the plate heat exchanger is disabled. When there is a demand for hot water the boiler will only operate when the flow of water through the boiler is greater than 2.3 l/m. This is sensed by a device called a flow switch. If the flow of water is below 2.3l/m the boiler not fire.

Winter / summer switch
If the winter/summer switch is in the ‘summer’ position the boiler will not operate in central heating regardless of the demand from internal/external controls.

System pressure
The boiler will not operate if the system pressure is below 0.4bar; this is because the boiler is fitted with a low water pressure switch to prevent the boiler being fired when system pressure is low. If the water pressure switch operates the boiler will ‘lockout’ the PCB and the display will show fault code L /E. To rectify this system pressure should be re-pressurised to 1bar and the rest button pressed.