Sequence Of Operation - IBC VFC 15-150 Manual

2.5
2-4
VFC 15-150 - VFC 45-225 MODULATING GAS BOILERS

seQuenCe oF oPeration

the control module has 5 cycles during normal operation, as well as an error
mode for problem detection:
standby cycle
1.
Purging
2.
3. ignition cycle
4. Heating cycle
5. Circulating cycle
error mode
6.
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. 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 preempted.
INSTALLATION AND OPERATION INSTRUCTIONS