Instruction manual

56
X. OPERATING (continued)
c. External Low Limit, Parameter ZC = ELL
The boiler control is capable of functioning as
a warm start control when external limit control
is installed that closes a contact when boiler
water temperature falls below a setpoint. When
an external limit contact closes (boiler water
is cold) the boiler is started and the ZC and C1
output terminals are de-energized. When the ZR
terminal is de-energized (boiler water temperature
is above setpoint) the call for heat is ended and
the C1 terminal is released to operation and the
ZC terminal is energized. An External Low Limit
Request is detected by sensing a voltage on the ZR
terminal. Refer to Table 14.
TABLE 14: EXTERNAL LOW LIMIT,
PARAMETER ZC_= ELL
Call for Heat Circulator Status
T-T
Input
ZR
Input
C1
Output
ZC
Output
off off off on
on off on on
on on off off
off on off off