TEMPRA 24
37
8. FAULT FINDING
Before beginning any fault fi nding 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 fi tted, must
all call for heat. This will cause the pump to run.
Internal Call for Heat: C.H. fl ow temperature sensor, 88°C high limit 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 fl ow temperature. When the central heating is satisfi ed the
burner will go off and the fan stops i.e. stand-by mode.
Note -
If the boiler thermostat is set to maximum then the burner pressure will go to maximum effectively
bypassing the auto range rating facility
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
8.03 PMF03F PCB
The PMFO3 PCB has fi vediagnostic 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 four lights indicate:
1
Boiler On Indicate
2
Boiler Shut down warning
4
Central heating standby (Flashing Light)
Central Heating circuit ON (Permanent Light)
5 Insuffi cient pressure in Central Heating System (Flashing Light)
Electric power supply ON (Permanent Light)
Note:
Always check for suffi cient gas supply (20mbar inlet working pressure for NG and 36mbar for LPG). Minimum
3 metres of 22 mm diameter pipework on C.H. fl ow and return with adequate by-pass. A correctly installed fl ue
system and a 3 amp fuse.
When operating the C.H. the following lights should be on: 4, 5 and fl ame on light.