High Limit Controller - Honeywell Aquasat L7224 A Aquasat L7224 C Manual

L7224A,C; L7248A,C,L OIL AND ELECTRIC BOILER
Table 4. Display readout definitions.
Text Description
Err Error Code (if one is present)
bT Boiler Temperature
HL 1
High Limit
HdF High Limit Differential
LL Low Limit (L7224 only)
Ldf Low Limit Differential (L7224 only)
tt Local Thermostat Status
ttE EnviraCOM Thermostat Status
brn B1 (Burner) output (ON or OFF)
Cir C1 (Circulator) output (ON or OFF)
ZC ZC (Zone Control) output (ON or
OFF)
Zr ZR (Zone Request) Call for HEAT
(ON or OFF)
ELL External Low Limit Enabled
(L7248L only)
duu ZR Configured as Domestic Hot
Water Request (L7224, L7248L
only)
ASC Anti Short-Cycle Timeout
bSP
Boiler Set-Point
dhc
DHW Module Connected
NO)
ot
Outdoor Temperature
otL
Outdoor Temperature Low
otH
Outdoor Temperature High
btL
Boiler Temperature Low
bP
Boost Period
bS 2
Boost Step
UUS Warm Weather Shutdown
Temperature
1
Display shows local setting; not the setting as modi-
fied by an external enviracom control.
2
Settings are viewable only if the outdoor reset mod-
ule and outdoor temperature sensor are installed
and functioning properly.
3
Settings are viewable only if the domestic hot water
module and sensor are installed and functioning
properly.
68-0281—18
2
3
(YES or
2
2
2
2
2
2
Operation
The L7224 and L7248 models can be in any of four
operational states: Normal, High Limit, Low Limit and
Display
Error. The controller moves back and forth from
Err
High Limit to Normal to Low Limit state as part of
normal operation. Only devices having High Limit
bt
settings are restricted to the High Limit and Normal
states. However, the controller will enter the Error state
HL
when there is an abnormal condition. The operating
states are:
HdF
1. Normal: Boiler temperature went below the High
Limit setting (minus the Differential) and has
LL
not exceeded the High Limit setting; or, the
boiler temperature went above the Low Limit
LdF
setting and has not gone below the Low Limit
tt
setting (minus the Differential); or, ZR input is
not powered with 120 Vac (only L7248L with
ttE
ELL set On).
2. High Limit: Boiler temperature went above the
brn
High Limit setting and has not dropped below
the High Limit setting (minus the Differential).
Cir
3. Low Limit: Boiler temperature went below the
Low Limit setting (minus the Low Limit Differen-
2C
tial) and has not gone above the Low Limit set-
ting; or, ZR input is powered with 120 Vac (only
2r L7248L with ELL set On).
4. Error: The controller has detected an error condi-
tion (e.g., open sensor) and has shut down the
ELL
burner output. The ZC output is energized. The
controller continues to monitor the system and
dvv
automatically restarts if the error condition
clears. Refer toTable 4.
The operating sequence for the L7224/L7248 is
ASC
shown in
Table 6–9.
bSP

High Limit Controller

dhc
The High Limit opens and turns off the burner when
the water temperature reaches the setpoint. The High
ot
Limit automatically resets after the water temperature
otL drops past the setpoint and through the Differential.
The L7248 models have High Limit Differential
otH
presets of 15 °F (8 °C). The L7224 models have High
Limit Differential presets of 10 °F (6 °C).
btL
Low Limit and Circulator
bP
Controller
bS
On a temperature rise, with the adjustable Differential
UUS
at the default setting of 10 °F (6 °C), the burner circuit
breaks and the circulator circuit makes (assuming no
call for heat is present) at the Low Limit setpoint. On a
temperature drop of 10 °F (6 °C) below the Low Limit
setpoint, the burner circuit makes and the circulator
circuit breaks. See Fig. 7.
6