Safety Thermostat; Function; Checks; Removal - Biasi GARDA M90F.24S Service Manual

17

Safety thermostat

17.1

Function

The safety thermostat A in Fig. 67 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.
Fig. 67
17.2

Checks

Warning: isolate the boiler from the mains
electricity supply before removing any
covering or component.
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.
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
32
A
contact must be closed (electrical resistance zero
Ω).
17.3

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 models M90F.28S and M90F.28SR, remove
the screw B and the plate C (Fig. 68).
Fig. 68
2 Disconnect the wiring D (Fig. 69).
Remove the spring E which holds the overheat
3
thermostat on the pipe of the primary heat ex-
changer and remove it.
D
Fig. 69
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.
C
B
E