Product specifications

ATMOS MULTI Mk 2 version 2008
Page 10
5.2 Operating principle
 No heat demand
The appliance will carry out a self-test when the
electrical supply is switched on and then once every
24 hours (if there has been no heat demand). For
this test, the boiler's integral central heating pump
will run for 3 minutes and the three-way valve will
switch to central heating in order to prevent the
pump from seizing.
 Meeting the heat demand (Continuous
Comfort mode)
When there is demand for heating and domestic hot
water at the same time, the appliance will generally
deal with both simultaneously. In this case, approx.
7 to 22kW (24/80), 9 to 29kW (32/80), or 10 to
34kW (38/80) is available for heating the home,
depending on the hot water demand. The three-way
valve is then set at the mid-position, so that one part
of the heated primary water is pumped to the
radiators and one part to the water heater. This
unique three-way valve output regulation prevents a
drop in the temperature of the home when the water
heater is heating up. The 'continuous comfort' mode
may be switched off if not required.
The central heating is controlled using a volt free
room thermostat. The domestic hot water
temperature is controlled by a 'User' setting, which
is adjusted via the control unit, and external
thermostatic mixing valve.
 Heat supply
When there is a demand for central heating, the
boiler's integral central heating pump and
combustion fan are automatically switched on.
Burner ignition occurs on the combustion fan
reaching its regulated speed. If no flame signal is
detected after 5 seconds, two more attempts for
burner ignition will be made within a 15-second
period, after which the appliance will shut down.
On loss of flame, the appliance will carry out two
restart attempts, after which the appliance will shut
down. If the temperature of the central heating water
reaches 90qC, the burner will automatically be
extinguished. The appliance has an anti-cycling time
of 3 mins during which the burner will not re-ignite.
This period may be changed via the control panel to
6 mins or, alternatively, switched off.
On reaching the heating demand, the burner will be
switched off, and the central heating pump
continues to run for a further one-minute period,
after which the three-way valve will switch to the
heat exchanger (ie. domestic hot water heating). The
pump will then run in hot water heating mode for 10
minutes (Factory setting). The pump running times
may be adjusted to suit individual system
requirements (see Appendix).
An insufficient heating water flow rate will be
detected by the high limit thermostat, which on
activation will cause the appliance to shut down.
 Combustion
The appliance is equipped with a continuously
modulating burner. The burner's heat input may be
manually set to suit individual system requirements.
Using the mechanical gas/air coupling, the burner
capacity can be controlled by adjusting the speed of
the fan. The appliance heat input automatically
reduces as the central heating flow temperature
reaches 80°C or higher.
 Most Efficient Start
Most Efficient Start is a comfortable energy saver,
which ensures that the home is heated as efficiently
as possible. When there is a central heating demand
the appliance always starts heating the home on a
low burner heat input. The amount of time at which
the burner continues to operate at low input depends
upon the heating demand of the heating system.
After either, first connecting the appliance to the
power supply, resetting following shut down, or
following a 180 minute period with no heat demand,
the burner will operate on a low heat input for 3
minutes, thereafter it is self adjusting.
 OpenTherm Modulating Thermostat
Instead of an on/off thermostat, an OpenTherm
modulating thermostat can be connected to the
control unit (see 7.13). In this case the desired CH
flow temperature is set by the thermostat.
 Weather-dependent control
(Not available if using an OpenTherm thermostat).
Using an extra kit available from Atmos,
comprising an external temperature sensor and a
central heating return temperature sensor, the Multi
can be easily controlled in a weather dependent
manner by changing a number of control settings.
 Comfort loop circuit
The Multi is equipped with a second independently
controlled heating circuit that can be used as a
comfort loop (eg. bathroom floor heating or towel
rail heating).