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SAfETy THERMoSTAT
19 SAfETy THERMoSTAT
19.1 function
The safety thermostat A in Figure 19.1 and Figure 19.2 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 tem-
perature of the primary circuit reaches a dangerous temperature,
the safety thermostat opens the electric circuit that supplies the
on-off operators of the gas valve.
Consequently, the full sequence ignition device attempts to light
the burner and, at the end, locks the boiler and lights the lock-out
signal lamp.
figure 19.1
A
19.2 Checks
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.
Warning: isolate the boiler from the mains electrici-
ty supply before removing any covering or compo-
nent.
Electrical function
1 Remove all the case panels and the lid of the sealed cham-
ber.
2 Disconnect the wiring B of 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 electrici-
ty supply before removing any covering or compo-
nent.
1 Remove all the case panels and the lid of the sealed cham-
ber.
figure 19.2
b
A
C
2 Disconnect the wiring B (Figure 19.2).
3 Remove the spring C which holds the overheat thermostat on
the pipe of the primary heat exchanger and remove it.
4 Reassemble the overheat thermostat carrying out the opera-
tions 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 com-
bustion analysis, refer to the appropriate chapter
Maintenance of the installation instructions manual.
