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37
AST 14 C 259/00
SAFETY DEVICES
Safety thermostat
Safety thermostat positioned onto bi-thermal heat exchanger is a normally closed contact.
When the water temperature value detected by thermostat is above 95 °C for CTFS
models or above 105 °C for CTN models, contact opens thus cutting off gas valve power
supply. Burner will be consequently turned off.
Safety thermostat triggering with gas valve powered results in boiler shut-down due to
"safety thermostat triggering" only if the opening status is above 4 seconds (non-volatile
shutdown). Should these conditions not be present, burner will turn off, but shut-down will
not be signalled.
Safety thermostat is acknowledged and managed only when it triggers during a burner
ignition request. So, should it be already open before the ignition request, this latter will be
delayed until thermostat contact is closed.
WARNING: to trigger at different temperatures, boilers feature different thermostats based
on the model (CTFS or CTN).
Air Pressure Switch
The pressure switch, assembled on forced draught models only, has a normally open
contact. It is used to detect the correct pressure difference in two different points of the
boiler, and it is directly managed by the electronic board.
Pressure switch contact shall be open before fan is powered, and closed when this latter is
working. At the end of the request, when fan is no longer powered, contact shall open
again. To this end, board makes a double check (starting and final) of contact opening.
When pressure switch is open, gas valve cannot be powered.
If the pressure switch contact is still open 10 seconds after combustion fan has been
powered, a volatile shut-down signal (not to be reset) is developed. The same shut-down
signal is developed if pressure switch is in a wrong position when boiler is working or in
stand-by condition. Boiler enters the non-volatile shut-down condition (to be reset) only
when pressure switch is in the wrong position for more than one minute.
Differential pressure switch: 45/35 Pascal Pmax=1500 Pa