ICI Caldaie RIO 140, Installation And Servicing Manual

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2 GENERAL BOILER INFORMATION
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Fig. 7
2.14 METHOD OF OPERATION
The boiler operating mode is controlled by the 'Heating' switch on the control panel. When set to Hot Water
Only, the boiler will only operate in the Domestic Hot Water mode. When set to Heating & Hot Water, it will
operate in the Domestic Hot Water and Central Heating mode.
Note : The timer only controls the operating times of the central heating, not domestic hot water - this is
available continuously.
Incorporated within the boiler case is an insulated unvented domestic hot storage cylinder containing 140
litres of domestic hot water maintained at the temperature set by the adjustable hot water temperature
selector and (depending on incoming mains pressure) available to the User at a maximum pressure of 3.5
bar.
Domestic hot water supply always takes priority over central heating. If a demand for hot water occurs during
a central heating period and reduces the store temperature to below that set by the hot water temperature
selector, the boiler automatically switches to the hot water mode until the stored water is reheated to the
temperature set by the hot water temperature selector. This interruption in the central heating should not be
noticed by the User.
Central Heating Mode - If there is a call for heat, i.e. the timer and room thermostat (if fitted) are calling for
heat, the pump will start to circulate the central heating water, activating the flow switch to start the ignition
sequence. After a few seconds the burner will light,
remaining on minimum output for approximately 90
seconds before gradually increasing to it's preset maximum.
The burner output is then automatically adjusted to match the system demand. When the temperature of the
primary water is equal to the pre-set temperature minus 10°C, the burner output is automatically reduced.
When the set water temperature is reached, the burner is turned off. The pump continues to run, circulating
water around the system, for as long as both the timer and room thermostat (if fitted) are calling for heat. As
the heating system water cools, the temperature drop is detected by the control system and the burner is
automatically restarted for the cycle to continue until either the timer or room thermostat stops calling for
heat. The burner is then turned off (if it is operating at the time) and the pump runs on for about 2½ minutes.
Domestic Hot Water Mode - When a demand for hot water reduces the temperature of the stored hot water
below that set by the adjustable hot water selector, the pump starts and the burner lights, increasing to its
maximum output. Water in the boiler is then diverted from the central heating system to reheat the stored hot
water to the temperature set by the adjustable hot water temperature selector. The burner output gradually
modulates down to its minimum output and remains at this output until the stored water reaches the selected
temperature, when the burner is turned off and the pump stops. The boiler then returns to the central heating
mode.
In both modes the fan (single speed) starts before the burner lights and stops after the burner is turned off.
The temperature display (see Fig. 14) gives an indication of the temperature of the water in the primary
circuit leaving the heat exchanger to either heat the store or the heating system. At temperatures upto 70°C
the burner operates at maximum output, above this temperature the output automatically modulates down to
suit the demand.