F4 Minimum gas pressure switch
F6 Air pressure switch
Y13 Main solenoid valve
Y12 Safety solenoid valve
1 Thermally-triggered safety shut-off valve ( installation by installer)
104 Gas pressure regulator
106 Filter
108 Gas ball valve (installation by installer)
119pBr Measuring point for gas outlet pressure
119.1 Measuring point for gas pressure in valve space
119.2 Air pressure measuring point
Description of functions
When the system is switched on for the
first time, after a power failure or safety
shutdown, after a lack of gas or after the
system has been out of operation for 24
hours, the pre-ventilation period of 24
seconds begins.
During prepurge period:
- blower pressure is monitored
- the combustion chamber is monitored for
flame signals.
At the end of the prepurge period:
- ignition is switched on.
- main and safety valve are opened.
- burner starts.
Monitoring
The flame is monitored by an ionisation
probe. The probe is insulated and
fitted to the gas head and is routed
through the flame disc into the flame
zone. The probe must not have any
electrical contact with earthed parts.
The burner switches to lock-out if a short
circuit occurs between the probe and
the burner earth.
During burner operation, an ionised
zone is produced in the gas flame
through which a rectified current flows
from the probe to the burner head.
The ionisation current must be at least 1,5
μA.
Safety functions
- If no flame is produced when the burner
is started (gas release), the burner will be
switched off at the end of the safety
period, lasting no more than 3 seconds,
and the gas valve will close.
- If the flame goes out during operation,
the gas supply is interrupted within one
second. A restart takes place. Once the
burner starts, operation is continued.
Otherwise, a safety lock-out occours.
- If there is a lack of air during reventilation
or operation, a safety lock-out occours.
- If there is a lack of gas, the burner does
not begin operation or switches off.
A waiting time of 2 minutes follows. This is
followed by a further start attempt. If there
is still no gas pressure, a further waiting
time of 2 minutes follows. The waiting time
can only be reset by interrupting the
power supply to the burner.
Waiting times: 3 x 2 min, then 1 hour.
In the event of controller shutdown
- Controller thermostat interrupts heat
request.
- Gas solenoid valves close.
- Flame goes out.
- Burner motor switches off.
- Burner is ready for operation.
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