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9
Sequence of operation
Table 1A_Sequence of Operation - Space Heating and DHW
1 Service (continued)
OPERATION DISPLAY
1. The manual reset high limit must be closed before any
action will take place.
HTR: Standby
OUT: 123.8F(129)
2. Upon a call for heat the control turns on the appropriate
pumps (system and boiler pumps for space heating; DHW
pump for DHW call). The flow switch and low water cutoff
(if equipped) must close.
HTR: Standby
OUT: 123.8F(129)
3. • The gas pressure switch(es) (if equipped) must close.
• The louver proving input must close.
• If the air pressure switch is open, the prepurge cycle then
begins by starting the combustion blower. Once started,
the air pressure switch must close.
HTR: Standby
OUT: 123.8F(129)
4. After the 15 second prepurge, the blower slows down and
the hot surface igniter (HSI) is energized. The HSI is heated
for at least 20 seconds.
HTR: PREPURGE
OUT: 123.9F(129)
5. Once the HSI is hot, the trial for ignition begins with the
opening of the gas valve.
HTR: IGNITION
OUT: 123.9F(129)
6. If the SMART SYSTEM control does not sense flame, then
it will lock out.
HTR: POSTPURGE, PREPURGE
OUT: 123.9F(129)
7. If the SMART SYSTEM control senses flame,
it will fire the burner to maintain the setpoint. The
stages will fire as required to hold the actual temperature at
the setpoint.
HTR: RUN STG: 1
OUT: 124.8F(129)
8. If the space heating call for heat is active, and the DHW
thermostat closes, the control will turn on the DHW pump,
wait 2 seconds, and then turn off the boiler pump. This will
divert the hot water away from the heating zone(s) and send
it to the DHW tank instead. The control will then fire the
stages to maintain the outlet temperature to the DHW boiler
setpoint.
HTR: DHW STG 123
OUT: 177.8(180)
Copper-fin II/IIE Boiler and Water Heater Service Manual