Biasi M90E.24S, Руководство по обслуживанию

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19 Safety thermostat
19.1 Function
The safety thermostat
A
in Fig. 77 is a device that
senses the temperature of the primary circuit water
which flows in the outlet pipe of the primary 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.
A
Fig. 77
19.2 Checks
Warning: isolate the boiler from the mains
electricity supply before removing any
covering or component.
n
Overheat temperature value
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.
n
Electrical function
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
W
).
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.
1b For model M90E.28S and M90E.32S remove the
screw
B
and the plate
C
(Fig. 78).
B
C
Fig. 78
2 Disconnect the wiring D (Fig. 79).
3 Remove the spring E which holds the overheat
thermostat on the pipe of the primary heat ex-
changer and remove it.
D
E
Fig. 79
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 refer to section Combustion
analysis check
in the chapter
Maintenance
of
the installation instructions manual.