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Differential. The L7248 models have High Limit
Differential presets of 15°F (8°C). The L7224
models have High Limit Differential presets of 10°F
(6°C).
Figure 24: Setpoints and Differentials
Action System Response
Thermostat
calls for heat.
Circulator starts when water temperature is
above Low Limit setting (if applicable). Boiler
temperature is checked. Burner starts when
water temperature is below High Limit setting.
Boiler exceeds
the High Limit.
Burner is turned off. Burner restarts when the
water temperature drops below the High Limit
setting minus the Differential.
Thermostat is
satised.
Circulator and burner turn off.
Error condition
1-5.
If an error condition is detected, all outputs ex-
cept ZC are shut down. Burner is off. Control
continues to function and restarts when error is
corrected.
During the error check sequence, the system
checks for drift in the sensor and corrosion in
the connections.
Error
condition 6.
EnviraCOM communication is not available.
Error
condition 7.
The control has reset the High Limit, Low Limit
and Differential setting to a default setting and
will continue to run at those settings.
Performance of the system will be degraded.
Error
condition 8.
If the error condition is detected, all outputs
except ZC are shut down. Burner is off. Control
continues to function and restarts when all
three user keys have been pressed longer than
60 seconds.
Table 5: L7224 / L7248 Controller
Operating Sequence
System Condition Diagnostic Condition Check Action
Boiler is cold, house is
cold.
Display is OFF. 120 Vac System power. Turn system power on.
Display is ON. 24 Vac T-T No 24 V; replace control.
24 V present; disconnect thermostat,
short T-T.
Boiler starts, check wiring and thermostat.
120 Vac at B1-B2 • If no, replace control.
• If yes, check burner and wiring.
Refer to Err on display. -----
Boiler is hot, house is
cold.
Display is ON. 120 Vac at C1-C2 • 120 Vac at C1-C2, check wiring
to pump.
• Wiring OK, is pump running?
• If not, replace the pump.
• If pump is running, check for
trapped air or closed zone valves
Boiler below the Low Limit tempera-
ture, wait for boiler to go above Low
Limit temperature.
-----
Boiler above LL? If yes, check for
120 Vac between ZC and L2.
• If no 120 Vac , replace control.
• If yes, check zone relays, circulators
and wiring.
Table 6: Trouble Shooting Guide
9. LOW LIMIT AND CIRCULATOR CONTROLLER
On a temperature rise, with the adjustable
Differential 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
Figure 24.