Ferroli F 24 B Instructions For Installation, Use And Maintenance Manual page 30

The burner will light at ignition burner pressure, automatically range rating itself up to the heating load,
then modulating down when the boiler reaches the desired flow temperature. When the central heating
is satisfied the burner will go off and the fan stops i.e. stand-by mode.
Note - If the boiler thermostat is set to maximum than the burner pressure will go to maximum
effectively bypassing the auto range rating facility
Domestic Hot Water Mode
External Call for D.H.W: Flow meter registers at least 2.5 litres/min flow to the hot water taps.
Internal Call for D.H.W: Low water pressure switch calling for heat.
If both internal and external calls are present the boiler follows the same sequence as for C.H. to light
the burner. However, for D.H.W. the burner will go straight to maximum and then modulate once the
water reaches the set temperature of the control thermostat. Turning the tap off will return the boiler
to stand-by mode.
Note: Following shut down of the D.H.W. or C.H. the boiler will go into a three minute central
heating delay.
Limit thermostats
T/Stat Location
Flue gas Secondary
safety heater
thermostat Exchanger
Frost Incorporated
in C.H.
Sensor
Overheat Top LHS
of Heat
Exchanger
The MFO3 PCB has fivediagnostic lights, each light corresponds to a particular function and will light in
turn as the boiler goes though its sequence of operations.
In order, the five lights indicate:
1 Boiler On Indicate
2 Boiler Shut down warning
3 Domestic Hot Water circuit ON
4 Central Heating standby (Flashing Light)
Central Heating circuit ON (Permanent Light)
5 Insufficient pressure in Central Heating System (Flashing Light)
Electric power supply ON (Permanent Light)
Note: Always check for sufficient gas supply (20mbar inlet working pressure for NG and 37mbar for
LPG). Minimum of 22 mm diameter pipework on C.H. flow and return with adequate by-pass. A correctly
installed flue system and a 3 amp fuse.
30
Function Nominal Operat-
ing Temperature
Protect boiler by 100°C
stopping ignition
and cuts power
to gas valve
Fires the boiler 7°C - 14°C
and runs pump to
maintain minimum
water temperature
Protect boiler by 100°C
stopping ignition
and cuts power
to gas valve
Ferroli F 24 B
Circuit Wiring Colours
240V AC Grey
Grey
Low voltage Red
DC Red
240V AC Grey
Grey