Product Features
Boiler Sequence
Boiler Control Instruction & Operation Manual
Page 6 of 68
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Boiler Sequence Status is shown on both the Home screen and the Status Screen. Once limits have been
established the boiler start/stop sequence progresses as show in the graph below;
Boiler
“Status”
Shown on Display:
Run
Stabilization
Time
Low Fire
Hold
Time
Slow
Start
Ramp
Released
to
Modulate
CH Maximum Modulation
Purge Rate
Postpurge
Rate
Minimum Modulation
Lightoff Rate
CH Low Fire Hold Rate
Slow Start Ramp Rate
Symbol Legend
Adjustable parameters are
shown in shaded box:
Adjustable Parameter
30s
4s 1 minute
CH Low Fire
Hold Time
Slow Start Enable
Slow Start Degrees
5 minute
Pump
Overrun
Time
(Note; refer to Parameter Adjustment for additional information.)
Figure 5: Central Heat Start sequence (Typical for Domestic Hot Water)
Table 3: Boiler Sequence
Status:
Description
Standby
Boiler is not firing.
Appropriate circulators are
“On” if “Priority” is not standby. There is a
Central Heat call for heat and the Supply temperature is greater than setpoint minus the
“Diff Below”.
Prepurge
When supply temperature drops below setpoint minus the
“Diff Below,” burner demand
continues with following Status shown:
Safe Startup
: Flame circuit is tested.
Drive purge
: The blower is driven to the fan purge speed.
Prepurge:
After the blower reaches the fan purge speed setting the 30 second
combustion chamber purge is conducted.
Direct
Ignition
After purge time is complete the following Status is shown:
Drive light-off
:
The blower is driven to light-off rate.
Pre-Ignition Test
: After the blower reaches light-off rate a safety relay test is conducted.
Pre-ignition
:
Spark is energized and it is confirmed that no flame is present.
Direct Ignition
:
Spark and Main fuel valve are energized.
Running
After the flame is proven the sequence continues with run stabilization and, when
selected, low fire hold time and slow start ramp. Once the field adjustable low fire hold
time and ramp rate is completed normal boiler operation begins, modulation rate
depending on temperature and setpoint selections.
Post-
purge
When the call for heat ends the main fuel valve is closed and the blower is driven to the
fan post-purge speed. After the blower reaches the fan post-purge speed setting the 5
minute second combustion chamber purge is conducted.
