Safety Thermostat; Function; Checks; Removal - Biasi Activ A 25C Service Manual

19

Safety thermostat

19.1

Function

The safety thermostat A in Fig. 19.1 is a device that
senses the temperature of the primary circuit water
which flows in the outlet pipe of the condensing heat ex-
changer.
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. 19.1
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.
A
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 Disconnect the safety thermostat and check its
electrical function. Normally (no intervention) the
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.
2 Disconnect the wiring B (detail in Fig. 19.2).
3 Unscrew the screws C and remove the overheat
thermostat.
Fig. 19.2
4 Reassemble the overheat thermostat carrying out
the operations in reverse order.
5 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.
B
C
41