IBC Technologies VFC 15-150 - Boiler Operational Sequence

IBC Technologies Inc. 25 VFC 15-150 and VFC 45-225
2.5 SEQUENCE OF
OPERATION
The control module has 5 cycles during
normal operation, as well as an error
mode for problem detection:
1. Standby cycle
2. Purging
3. Ignition cycle
4. Heating cycle
5. Circulating cycle
6. Error mode
Each state is explained below. A flow
chart for the sequence of operation can
be found in the back of the manual.
GLOSSARY OF TERMS
This glossary briefly defines some terms
used in the Sequence discussion.
Call for Heat
The thermostat indicates that room
temperature is below the thermostat
setting.
Heat Required
Temperature sensors on the boiler
indicate that water temperature is below
the water temperature target or setpoint.
Heating Enabled
The boiler is powered and there is a
Call for Heat, Heat is Required, and in
certain instances a prescribed time
interval has elapsed since the previous
heating cycle. The boiler will start and
enter the Heating Cycle unless it is in an
error mode.
2.5.1 Standby
Waiting for a Heating Enabled signal.
The burner and boiler pump are off
during this time.
2.5.2 Purging
Prepurge
On a Heating Enabled signal, the boiler
automatically enters a prepurge cycle.
The fan starts and automatically adjusts
to a level suitable for ignition. Ten
seconds later, the pump starts. After a
total of 15 seconds, the ignition cycle
begins.
Interpurge
The boiler enters an interpurge cycle if
ignition is unsuccessful. The fan and
pump continue to run, and ignition is
delayed by an additional 15 seconds.
Postpurge
The fan remains on for 20 seconds and
then reduces airflow to an ultra low
flow mode for 90 minutes unless pre-
empted.
The pump remains on for 5 minutes
(adjustable) after the heating cycle
ends.
If the heating cycle ends as a result of
water temperature exceeding the load
specific band limit, the postpurge will
continue as normal, but the boiler will
enter the circulating mode.
The cut off temperature levels are
specific for each load; they are
determined using the preset target plus
½ of the supply differential entered.
Default values for such differentials are
22°F (+/- 11°F) for space heating with
outdoor reset and 40°F ( +/- 20°F) for
DHW and other set point loads,
If there is a Heating Enabled signal any
time during this cycle, the postpurge
ends, and a prepurge begins, otherwise
the boiler will enter Standby mode.
2.5.3 Ignition
After the prepurge, the gas valve opens
for 4.0 seconds.
If no flame is detected at the end of the
trial, the interpurge cycle is entered. If
ignition fails 3 times successively, the
boiler locks out for a 1 hour long