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3.1 Boiler Operation
1. Switched Live On: When switched live is supplied to
the boiler and the flow temperature is less than the set
point the sequence below commences.
2. Flow Switch: After 10 seconds if the flow switch has
made then fan pre-purge occurs. After 10 seconds if
the flow switch has not made then anti-cycle occurs.
3. Fan Pre-Purge: The flow switch is made and the fan
is on while the spark generator and gas valve are off.
After 5 seconds ignition occurs.
4. Ignition: The flow switch is made, fan, spark
generator and gas valve are on. If a flame is detected
then burner on occurs. If a flame is not detected within
5 seconds and less than 5 ignition attempts have been
made then fan purge occurs. If a flame is not detected
within 5 seconds and 5 ignition attempts have been
made then ignition lockout occurs.
5. Burner On: The flow switch is made, fan and gas
valve are on while the spark generator is off. Flow
temperature is controlled by varying the fan speed (and
thereby the gas rate) to achieve optimum operation. If
the flow temperature is greater than the set point or
the TRVs all shut down then fan post purge occurs.
6. Fan Post Purge: The fan is on while the spark
generator and gas valve are off. After 5 seconds if the
TRVs are shut down then anti-cycle occurs.
7. Anti-cycle: The fan, spark generator and gas valve
are off.
8. Ignition Lockout: The fan, spark generator and gas
valve are off. The boiler can only be reset by manually
using the reset button.
9. Condensate Pump: Condensate accumulates in a
reservoir within the pump assembly. The pump may
run at any time, independent of boiler operation, to
discharge the condensate to drain.
3.0 Boiler Operation
8
© Baxi Heating UK Ltd 2011
Mains On.
Flow
temperature less
than set point ?
YES
5 second
Fan Pre-Purge.
Flame Detected ?
Burner On.
Ignition
Lockout.
5 second
Ignition Period.
All TRVs
shut down ?
Ignition done and
5 attempts made ?
Ignition done
and less than 5
attempts made ?
System Pump
Running and Flow
switch made ?
NO
YES
YES
YES
All TRVs
shut or Flow temperature
greater than set point ?
5 second
Fan Post Purge.
3 minute
Anti-cycle.
YES
YES
YES
Condensate Pump will
operate as necessary (3.1.9)