How Vortex Condensing Boilers Work; Vortex Heating System Design Considerations; Central Heating Mode; Domestic Hot Water Mode - Grant Combi 70 V3 User's Installation Manual

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 (Combi V3 and Combi
Max) - 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 plate 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.
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.
Domestic Hot Water Mode (Vortex Combi) - When a
demand for hot water (by opening a hot tap, etc.) is sensed
by the flow switch, the Hot Water pump starts and
circulates water from the store through the hot water plate
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 the water temperature does not exceed 65°C.
When the hot tap is closed and the flow switch senses that
hot water is no longer required, the Hot Water pump will
continue to run and the burner continues to fire until the
primary store temperature control is satisfied.
5 - GENERAL BOILER INFORMATION
Combi V3, Combi Max and Vortex Combi models
If the Heating switch is set to either TIMED or
CONSTANT, the boiler will return to the central
heating mode, with the Heating pump and burner
running. Note - As the temperature of the boiler is now
higher than the boiler thermostat setting the burner
may not fire immediately, but only after the flow
temperature has fallen to below the thermostat setting.
If the Heating switch is set to OFF, or the timer is in an
OFF setting, the Heating pump will not operate.
For optimum performance the thermostatic blending
valve has been factory set to provide a hot water
temperature of approximately 50°C.
If the water in the boiler is already up to temperature
when a hot tap is opened, there will be a delay before
the burner fires to maintain the hot water temperature
in the boiler (to heat the hot water).
5.19

How Vortex condensing boilers work

During the combustion process, hydrogen and oxygen
combine to produce heat and water vapour. The water
vapour produced is in the form of superheated steam in
the heat exchanger. This superheated steam contains
sensible heat (available heat) and latent heat (heat
locked up in the flue gas). A conventional boiler
cannot recover any of the latent heat and this energy is
lost to the atmosphere through the flue.
The Vortex Combi condensing boilers contain an extra
heat exchanger which is designed to recover the latent
heat normally lost by conventional boilers. This is done
by cooling the flue gases to below 55°C, thus extracting
more sensible heat and some of the latent heat.
To ensure maximum efficiency, the boiler return
temperature should be 55°C or less, this will enable the
latent heat to be condensed out of the flue gases. The
boiler will achieve nett thermal efficiencies of 100%.
To achieve maximum performance from a Vortex Combi
boiler, it is recommended that the heating system is
designed so that a temperature differential of 20°C
between the flow and return is maintained.
The boiler will however still operate at extremely high
efficiencies even when it is not in condensing mode and
therefore is suitable for fitting to an existing heating
system without alteration to the radiator sizes. The boiler
is capable of a maximum flow temperature of 80°C.
5.20

Vortex heating system design considerations

To achieve the maximum efficiencies possible from a
Vortex boiler, the heating system should be designed
to the following parameters:
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