Safety Thermostat; Function; Checks; Removal - Biasi RIVA COMPACT M90E.24S Service Manual

18

Safety thermostat

18.1

Function

The safety thermostat A in Fig. 1 is a device 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. 1
18.2

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
A
contact must be closed (electrical resistance zero
Ω).
18.3

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. 2).
Fig. 2
2 Disconnect the wiring D (Fig. 3).
Remove the spring E which holds the overheat
3
thermostat on the pipe of the primary heat ex-
changer and remove it.
D
Fig. 3
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
35