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Signal from the
flow switch
HOT WATER
DEMAND
(Overrides all other
overrun modes
and functions)
No demand and
primary
temperature below
6°C monitored by
the central heating
sensor
Internal
"Autofrostat"
Demand
Run pump
Below 4°C
Above 8°C
4°C to 8°C
Monitor central
heating sensor
Burner pressure
at 1.0 mbar
6
Burner pressure adjusted
based on the temperature
rise over the previous
minute. Aiming at 4°C
rise/minute.
Burner never to be
extinguished
irrespective of the
rate of temperature
rise
At the set point
change to a wide
band proportional
control
Commence normal central
heating mode until heating
temperature reaches 20°C
Return to normal
OFF state
Pump on until
primary temperature
drops to 50°C
No demand and central
heating temperature above
50°C monitored by the
central heating sensor
End of hot water demand
with no central heating
demand. Hot water
thermistor above 40°C
6 second pump pulse with a
2nd 6 second pump pulse 2
minutes later.
End of demand or central
heating temperature above
70°C monitored by the
central heating sensor
Fan on for
4 minutes
Inhibit operations
for approximately
1 second. 6 second
delay before re-
ignition from any
other demand.
Is the central
heating mode
interrupted?
AUTOMATIC
START-UP
SEQUENCE
HOT WATER
DEMAND
SATISFIED
Pump OFF
Wait for hot water
temperature to
drop to factory
pre-set level
Gas valve OFF.
Fan remains ON
Hot water
temperature above
70°C
Modulate heat
input to maintain
hot water
temperature at the
factory pre-set
level
Gas valve OFF
Fan overrun
4 minutes
Operating
Switch (or
programmer
OFF)
Domestic hot water
temperature
monitored by hot
water sensor
3. "Autofrostat" Function
4. Pump Overrun Function
5. Fan Overrun Function
2. Domestic Hot Water Mode
6. Central Heating ramp control
Pump pulse 6
seconds then 2
minutes later
2nd pulse