IBC VFC 15-150 Manual

2-5
BOILER SYSTEMS AND OPERATION
VFC 15-150 - VFC 45-225 MODULATING GAS BOILERS
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
specicbandlimit,thepostpurge will continue as normal, but the boiler will enter
the circulating mode.
Thecutofftemperaturelevelsarespecic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ame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 interval,
after which the ignition cycle is refreshed (e.g. for 3 further attempts). Alternately,
the boiler can be powered down and restarted to accelerate the re-try sequence.
The homeowner should follow up persistent recurrence of the 1 hour reset
routinebycontactingaqualiedservicetechnician,toevaluatethecauseofsuch
ignition irregularity.
With a successful ignition, the output of the boiler decreases immediately to a low
level, and the heating cycle begins.
2.5.4 Heating
The heating cycle lasts until the Heating Enabled state ends (for all loads),
or until water temperature exceeds the target temperature by ½ of the supply
differential for the last served load and the throttle has fallen to the minimum
output. At the end of the heating cycle, the boiler enters a postpurge.
Duringtheheatingcycle,theboileraddressesthemultipledenedloads
in accordance with its Prioritization algorithm. See Section 2.6.1. Boiler
output changes to meet heating demands as indicated by the temperature
characteristics of the boiler supply and return water. Boiler supply water
temperature targets vary according to the set up parameters entered, and are
subject to further variation for loads where Outdoor Reset has been selected.
Where thermal loads are within the boiler’s 15 to 150 MBH throttle range, the
control algorithm seeks to regulate the boiler supply temperature within ±3°F
of the target temperature. On/Off differentials apply to loads below the 15 MBH
minimum input rating. The following default differentials are automatically applied
upon initial load characterization: DHW and other SetPoint loads (±20°F); space
heating with Outdoor Reset invoked (±11°F). These default differentials can be
adjusted in the password protected Installer access area.
2.5.5 Circulating
This cycle operates when water temperature exceeds target by 1/2 of the supply
differential for that load at minimum output, and call for heat is still present. After
entering a postpurge, the system pump remains on until water temperature is
1/2 of the supply differential below setpoint temperature.
The boiler can also enter the Circulating mode during transition from a high

IBC VFC 15-150 Specifications

General

Brand	IBC
Model	VFC 15-150
Category	Boiler
Language	English