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HIGH LIMIT
SETTING
L7224: 10°F (6°C)
DIFFERENCE
L7248: 15°F (8°C)
DIFFERENCE
LOW LIMIT
SETTING
10ºF (6ºC)
DIFFERENCE
WHEN WATER REACHES LOW LIMIT SETTING, THE BURNER SHUTS
1
OFF OR THE CIRCULATOR PUMP STARTS (WHEN CALLING FOR HEAT).
Fig. 7. Setpoints and differentials.
Anti Short-Cycle Feature
The Anti Short-Cycle feature allows for field selection
of a delay time between burner cycles. Should a call
for heat occur following the end of the previous heat
cycle and before the Anti Short-Cycle delay time is
expired, the circulator will be allowed to run, but the
burner will be held off until the time has elapsed. The
range of the Anti Short-Cycle time is from OFF to five
minutes.
NOTE: This feature is blocked if a Domestic Hot
Water demand occurs. Domestic Hot Water
demands are serviced immediately, without
any delay.
NOTE: When the Aquastat is connected to the oil pri-
mary and/or thermostat via the EnviraCOM
bus, the Anti Short-Cycle time does not apply
to recycle events such as loss of airflow or
flame. It applies only to loss of demand.
ZR-Domestic Hot Water (DHW)
Request
The ZR terminal can be selected to service an indirect
water heater heat request. This parameter is set via the
3 digit display (see Adjusting Settings section of this
document). A heat request via the ZR terminal will
have priority over all other features such as the Anti
Short-Cycle feature or those enabled by the Outdoor
Reset Module (See form #69-2335 for more
information).
Parameter name
Boiler temperature drop
Thermal purge temperature limit
Thermal purge temperature rate of
drop
Thermal purge time delay
SWITCH BREAKS ON
TEMPERATURE RISE.
BURNER TURNS OFF.
CIRCULATOR OPERATES
ON A CALL FOR HEAT.
SWITCH MAKES ON
TEMPERATURE FALL.
BURNER OPERATES ON A
CALL FOR HEAT.
WITH NO HEATING
DEMAND, SWITCH BREAKS
ON TEMPERATURE RISE.
1
SWITCH MAKES ON
TEMPERATURE FALL,
BURNER IS ON TO
MAINTAIN MINIMUM
WATER TEMPERATURE.
CIRCULATOR IS OFF.
M23364
Table 5. Thermal Purge Settings.
Minimum value
Not adjustable
120 °F (or OFF)
Not adjustable
1 minute
L7224A,C; L7248A,C,L OIL AND ELECTRIC BOILER
Frost Protection
The Frost Protection function protects the boiler and
potentially the boiler plumbing from possible damage
which may occur should the water in the system begin
to freeze. The Frost Protection feature is enabled only
in the L7248 (cold start models). The feature default
setting is enabled (ON), but can be disabled using the
3-digit display. See "Adjusting Settings" on page 5.
When the Boiler temperature drops to the Frost
Protection Limit temperature (fixed 40 °F), the burner
is forced on. The Circulator and ZC outputs remain in
the same state as before the Frost Protection function
was enabled. They can be either ON or OFF during the
Frost Protection cycle.
When the Boiler temperature reaches the Frost
Protection Limit temperature plus a fixed 10 °F
differential, the burner is turned off unless requested
to stay on due to a different demand.
Thermal Purge Operation
The intent of thermal purge is to insure usable
residual heat in the boiler is circulated until it is
sufficiently depleted from the system before the
burner is allowed to fire. To that end, on a call for heat,
the burner is held off while the circulator runs until the
boiler temperature drops to the thermal purge
temperature or a time delay is exceeded. Both of these
parameters are adjustable. When the boiler
temperature reaches the thermal purge temperature,
the burner is allowed to fire. Thermal purge is only
applied to cold start Aquastat models (L7248) and will
not interfere with domestic hot water call for heat or
boilers equipped with Honeywell outdoor reset
accessories. For warm start models where a Low Limit
must be set, thermal purge is not applied.
In addition to the thermal purge temperature and
thermal purge time delay parameters, two other
conditions release the Aquastat from thermal purge in
order to maintain comfort in the space:
• The boiler temperature has dropped 10 °F from the
beginning of the thermal purge.
• Boiler temperature is cooling at a rate greater than
5 °F/minute while the circulator is running.
The thermal purge feature applies to single zone as
well as multi-zone applications.
Thermal Purge Settings
Some thermal purge parameters are configurable
using the 3 digit display. See "Adjusting Settings" on
page 5. Thermal purge may be disabled by setting the
thermal purge temperature limit to "OFF".
Maximum Value
Not adjustable
160 °F
Not adjustable
10 minutes
7
Default
10 °F
140 °F
(L7248)
5 °F/minute
2 minutes
68-0281—18
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