Ferroli F24
38
8.04 Temperature sensors (thermistors)
Identical, but individual, negative temperature co-efficient (NTC) thermistors are fitted in the C.H. and D.H.W. outlets
from the heat exchanger. As the water temperature increases the resistance in the thermistor decreases. This causes
the PCB to reduce the voltage to the modureg, in turn reducing the burner pressure. The wiring for each thermistor
is colour coded red for C.H. and blue for D.H.W. The sensors are fitted in wet pockets.
8.05 Limit thermostats
Two surface mounted auto reset bi-metal thermostats are located on the heat exchanger secured by spring
clips. Heat sink compound is used.
8.06 Main printed circuit board
Secured by flour plastic tabs the PCB is situated inside the control compartment. The transformer for low voltage
AC is attached to the PCB as is the DC rectifier. Potentiometers control C.H. output and maximum D.H.W.
temperature, both are adjustable by the controls on the facia and because the boiler features automatic
range rating no adjustments need to be made. Electro mechanical relays control pump operation and
put switched live to the ignition PCB (demand relay), they have transparent plastic covers so that their
contacts can be seen moving.
8.07 Air pressure switch
Operating at 230 V AC and situated next to the fan. Different coloured tubes connect the switch to the fan. It is a
make on pressure switch and only uses two terminals, the middle terminal is not used.
8.08 Short spares list
KEY NO. DESCRIPTION PART NO. G.C. NO.
(from fi g 2 )
14 Safety Valve C/W Manifold 805880 E39-485
16 Fan assembly 800480 E23-851
34 Central Heating Flow Temperature Sensor 800320 E23-839
42 Domestic Hot Water Flow Temperature Sensor 800320 E23-839
43 Air Pressure Switch 800150 E23-840
44 Gas Valve - VK4105G 808000 E23-768
49 Overheat Safety Thermostat 100°C 801240 386-815
50 High Limit Thermostat 88°C 800160 386-577
81 Ignition Electrode 806258 E26-348
82 Flame Sensing Electrode 801438 E23-855
136 Flow Meter C/W Elbow 805910 E39-465
Main PCB MF03 805900 E39-470
27 Heat Exchanger 807480 E77-470
