65
110327-07 - 2/23
ALTA
Combi Installation, Operating & Service Instructions
12. Priority Demand
Control accepts a call for heat from multiple
places and responds to its "Priority". When more
than one demand is present, higher priority
demand is used to determine active boiler
settings. For example, when DHW has priority,
setpoint, "Diff Above", "Diff Below" and pump
settings are taken from DHW selections. Active
"Priority" is displayed on the Diagnostic Menu,
item "
CO2
", see Table 16-9.
Boiler Protection Features
1. Supply Water Temperature High Limit
Control is equipped with internal operating
control and high limit features. Control monitors
a dual element temperature sensor that is UL353
and UL1998 listed. If supply water temperature
increases above the active setpoint plus diff
above, (default 190°F [87.7°C]) boiler is cycled
off. If temperature exceeds 210°F (98.9°C), a
manual reset hard lockout results. If boiler is
responding to internal Multiple Boiler Control
Sequencer, Header Sensor or an External EMS
demand and supply water temperature increases
above 190°F (87.7°C) control begins to reduce
the blower maximum speed setting and if the
temperature increases to 200°F (93°C) a forced
recycle results.
16
Operation
(continued)
Table 16-18: Order of Priority
CO2
Boiler Responding to:
1st Domestic Hot Water
2nd Sequencer Control
Connected to the peer-to-peer network.
3rd Central Heat 1
CH1 call for heat is on and there is no DHW
demand or DHW priority time has expired.
4th Central Heat 2
CH2 call for heat is on and there is no Central
Heat 1 or DHW demand.
5th Frost Protection
Frost Protection is active and there is no
other call for heat. Frost protection will be a
higher priority than Sequencer Control if the
Sequence Master has no active call for heat.
6th Urgent calibration
Performed because of no regular CH
demands and boiler is cold.
7th Boiler Switch "On/Off"
When Boiler Switch is set to "Off" position the
boiler does not respond to any demands.
2. High Differential Temperature Limit
Control monitors temperature difference between
return and supply sensors. If this difference
exceeds 58°F (32°C) control begins to reduce
blower maximum speed and if temperature
difference exceeds 63°F (35°C) a forced boiler
recycle results. Boiler will restart automatically
once temperature difference has decreased and
minimum off time has expired.
3. Return Temperature Higher Than Supply
Temperature (inversion Limit)
Control monitors supply and return temperature
sensors. If return water temperature > supply
water temperature for longer than a limit time
delay control shuts down and restarts boiler and
delays. If inverted temperature is detected more
than five times, boiler manual reset Hard Lockout
is activated.
4. External High Limit
An external limit control can be installed on low
voltage connections terminal strip. Be sure to
remove jumper when adding an external limit
control to system. If external limit opens, the boiler
will shut down and an open limit indication and
error code is provided. If limit installed is a manual
reset type, it will need to be reset before boiler will
operate.
5. External (LWCO)
An external LWCO control (optional) can be
installed on the low voltage connections terminal
strip 24 VAC LWCO connection. If the LWCO
opens, boiler will shut down and an open limit
indiction and error code is provided. If LWCO
installed is a manual reset type, it will need to be
rest before boiler will operate.
6. Boiler Mounted Limit Devices
Control monitors thermal fuse (top of heat
exchanger) and boiler water flow switch. If either
of these limits open while the boiler is running,
boiler will shut down and a fault indication is
provided. Additionally, control monitors an air
pressure switch. During boiler start sequence,
control requires the air pressure switch to be
in "open" position before blower starts and in
"closed" position after blower starts. If this does
not happen, start sequence is halted and fault
indication is provided. Air pressure switch is
only required to be closed during pre-purge. It
is normal for the air proving switch to be open
during run mode.
