21
Combi 70 & Combi 90 Oil Boilers
Method of operation
3.16
3 - GENERAL BOILER INFORMATION
Once the boiler is switched on (amber neon on) it will
always provide domestic hot water upon demand. The
timer only controls the operating times of the central
heating. When central heating is not required, the timer
switch should be set to OFF.
Domestic hot water supply always takes priority over
central heating. If a demand for hot water occurs
during a period of central heating, the boiler mode will
automatically change to provide hot water until the
demand ceases. This interruption in the central heating
only lasts for as long as hot water is required and
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
and the burner will light. When the temperature in the
boiler reaches that set on the boiler thermostat, 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 boiler thermostat and the burner is
automatically restarted for the cycle to continue until
either the timer or room thermostat stops calling for heat.
The burner and pump are then turned off.
Domestic Hot Water Mode - When a demand for hot
water (by opening a hot tap, etc.) is sensed by the
diverter valve flow switches, the pump starts and the
water in the boiler is diverted through the domestic hot
water heat exchanger, heating the incoming mains
water. The hot water produced is mixed in the
thermostatic blending valve with incoming mains
water to automatically ensure that the temperature does
not exceed 65°C.
Note: For optimum performance it is recommended that
the thermostatic blending valve is set to provide a hot
water temperature at the outlets between 45 and 50°C.
Note: If the water in the boiler is already up to
temperature, there will be a delay before the burner
starts to maintain the water temperature in the boiler.
When the hot tap is closed and the diverter valve flow
switches sense that hot water is no longer required, if
the timer switch is set to either TIMED or
CONSTANT, the boiler will return to the central
heating mode, with the pump and burner running. If
the switch is set to HOT WATER ONLY, the pump is
turned off but the burner will continue to run for a
short period until the water in the boiler reaches the
required temperature ready for another hot water
operation.
4 - BOILER INSTALLATION
Unpack the boiler
4.1
Prepare the wall
4.2
1 Carefully remove the packaging from the boiler
and remove it from the transit pallet.
2 Open the boiler door (open from the right hand
side) and remove the literature pack.
3 Lift off the two parts of the case top and remove
the water connecting pipework and fittings.
See Figs, 13, 13a and 14
If the boiler is to be used with a balanced flue, make
the hole in the wall for the flue as shown in Fig. 13 or
13a (low level flue) or Fig. 14 (high level flue).
Note: Dimensions A and B given in Figs. 13, and 14
include an extra 10 mm over the size of the terminal to
provide clearance for fitting.
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