G.
An external limit control can be installed between
terminals 5 and 6 on the terminal strip. Be sure to
remove the jumper between terminals 5 and 6 when
adding an external limit control to the system. If the
external limit opens, the boiler will shut down and error
code “b 26” will be displayed. If the limit installed is
a manual reset type, it will need to be reset before the
boiler will operate.
H.
The sequence of operation for a Alpine Series boiler
on a call for heat from a thermostat is as described
below:
1. When power is first turned on, 120V is provided
to the MCBA, the combustion fan and the LWCO
transformer. A separate 50VA transformer,
connected directly to the MCBA, powers all other
low voltage circuits.
2. For the first few seconds after power-up the control
module goes through a self check.
3. When there is a call for heat, the control module
checks to make sure the air pressure switch is
open. If it is, the combustion fan will be energized
and will ramp up to ignition speed. When the air
pressure switch closes, a 10 second prepurge is
activated.
4. After the prepurge, the control module energizes
the gas control valve and the spark for 4.5 seconds.
If a flame is established and proved, the control
allows the flame to stabilize for 5 seconds at the
combustion fan ignition speed setting. If the flame
fails to prove, the control module will attempt to
light the burner 4 more times. If a flame is still not
established, the control will lockout.
5. Once the flame stabilization period has ended,
the MCBA allows the burner to modulate. The
actual firing rate is dependent upon the measured
current and recent differences between the set point
temperature and the supply temperature. If an
outdoor sensor is connected to the control module
and the boiler is responding to a call for heat, the set
point temperature will be determined by the outdoor
reset curve shown in Figure 51.
6. Once the set point temperature is reached, the
MCBA will turn the burner off and allow the
combustion fan to operate in postpurge for 30
seconds before it turns off.
7. The central heating pump will continue to operate
until the room thermostat has been satisfied.
8. A demand for domestic hot water (DHW) is given
priority on Alpine Series boilers. If a call for DHW
is received while the boiler is responding to a call
for heat, the heating circulator is de-energized until
the call for DHW is satisfied.
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