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Installation & Operation Manual
55
7 Operating information (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. • If the unit is equipped with a proof of closure valve, the
proof of closure switch must be closed. The proof of
closure valve is then energized. The gas pressure
switch(es) (if equipped) must close.
• If the contact for the louvers is closed, the louver proving,
and auto reset high limit (water heater only) inputs 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, LOCKOUT
OUT: 123.9F(129)
7. If the SMART SYSTEM control senses flame, it will fire the burner
to maintain the set point. The firing rate will stage as required to
hold the actual temperature at the set point. If the boiler lights due
to a space heating call for heat, and the ramp delay function is
active (default is disabled), the staging will be held to a series of
increasing limits after the burner has lit.
HTR: RUN STG: 1
OUT: 124.8F(129)
8. If the space heating call for heat is active, and a DHW call for
heat becomes active, 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 modulate to maintain the outlet
temperature to the DHW boiler set point.
HTR: DHW STG 123
OUT: 177.8(180)
9. If the DHW call for heat remains active for more than 30 minutes,
and the space heating call for heat is also on, then the control will
turn on the boiler pump, turn off the DHW pump after 2 seconds,
and resume firing based on the space heating set point. As long
as both the space heating and DHW calls for heat remain active,
the control will switch back and forth between the two modes until
one of them is satisfied.
HTR: RUN STG 12
OUT: 123.0F(129)
10. Once both calls for heat are satisfied, the control will turn
off the burner. The blower will remain on for the 30 second
postpurge cycle. Any pumps that are running will continue to run
for their respective pump delay times, then turn off.
HTR: POSTPURGE
OUT: 127.4F(129)
11. Boiler pump off, system pump continues its delay if longer.
HTR: Standby
OUT: 124.7F(129)
12. System pump off.
HTR: Standby
OUT: 122.9F(129)
Sequence of operation