Safety Thermostat; Function - Biasi Parva HE M96.24SM/P Service Manual

19

Safety thermostat

19.1

Function

The safety thermostat A in Fig. 84 and Fig. 85 is a de-
vice that senses the temperature of the primary circuit
water which flows in the outlet pipe of the primary heat
exchanger.
If the temperature control system of the boiler fails and
the temperature of the primary circuit reaches a dan-
gerous temperature, the safety thermostat opens the
electric circuit that supplies the on---off operators of the
gas valve.
Consequently, the full sequence ignition device at-
tempts to light the burner and, at the end, locks the
boiler and lights the lock ---out signal lamp.
Fig. 84
19.2 Checks
Overheat temperature value
n
1 Set the temperature control knobs to their max.
position and run the boiler in d.h.w. and c.h.
2 Allow the boiler to reach its maximum operating
temperature (monitor the temperature gauge on
the instrument panel). The boiler should maintain
a temperature below that of the safety thermostat
and no overheat intervention should occur.
Warning: isolate the boiler from the mains
electricity supply before removing any
covering or component.
Electrical function
n
1 Remove all the case panels and the lid of the
sealed chamber.
2 Remove the screws B and the plate C (Fig. 85).
3 Disconnect the safety thermostat and check its
electrical function. Normally (no intervention) the
A
contact must be closed (electrical resistance zero
Ω).
19.3 Removal
Warning: isolate the boiler from the mains
electricity supply before removing any
covering or component.
1 Remove all the case panels and the lid of the
sealed chamber.
Remove the screw B and the plate C (Fig. 85).
2
B
Fig. 85
Disconnect the wiring D (detail in Fig. 86).
3
Remove the spring E which holds the overheat
4
thermostat on the pipe of the primary heat ex-
changer and remove it.
Fig. 86
5 Reassemble the overheat thermostat carrying out
the operations in reverse order.
6 Apply an adequate quantity of heat conducting
compound between the pipe and the thermostat.
Warning: After cleaning or replacement as
detailed above, if it deemed necessary to
undertake a combustion analysis, refer to
the appropriate chapter Maintenance of the
installation instructions manual.
A
C
D
E
37