FALCON II
31
8.0 FAULT FINDING
Before beginning any fault finding ensure that gas, water and electricity are available.
WARNING
: DO NOT link any terminals on block X10 or X11 as this will damage the PCB beyond repair.
8.01 Operating Sequence
With the power established the boiler is in its stand-by mode i. e. power on but no demand. The operational
sequence for C.H. and D.H.W. are as follows:
Central Heating Mode
External Call for Heat:
The temperature regulator, built in or remote clock and room thermostat, if fitted, must
all call for heat. This will cause the pump to run.
Internal Call for Heat:
C.H. flow temperature sensor, 88°C high limit and low water pressure switch all calling for
heat. If both external and internal calls for heat are present the MF03 PCB will energise.
In demand the fan will go to high speed causing the air pressure switch to operate. If the overheat (100°C) stat is
closed circuit the ignition will operate and the gas valve will be energised.
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:
Hot water flow temperature sensor 88°C high limit stat and 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.
8.02 Limit thermostats
T/Stat Location Function Nominal Circuit Wiring
Operating Colours
Temperature
C.H. Limit
Top RHS Shuts downmain 88°C Low voltage Blue
of Heat burner if boiler DC Brown
Exchanger thermostat fails
Frost
Incorporated Fires the boiler 7°C - 14°C Low voltage Red
in C.H. and runs pump to DC Red
Sensor maintain minimum
water temperature
Overheat
Top LHS Protect boiler by 100°C 240V AC Brown
of Heat stopping ignition Blue
Exchanger and cuts power
to gas valve
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.
