Installation & Operation Manual
7 Operating information (continued)
Sequence of operation
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1. | The manual reset high limit must be closed before any action will | HTR: | Standby | ||
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| OUT: 123.8F(129) | |
2. | Upon a call for heat the control turns on the appropriate pumps | HTR: | Standby | ||
| (system and boiler pumps for space heating; DHW pump for DHW | ||||
| call). The flow switch and low water cutoff (if equipped) must | OUT: 123.8F(129) | |||
| close. |
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3. | • If the unit is equipped with a proof | of closure | valve, the |
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| proof of closure switch must be closed. The proof of |
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| closure valve is then energized. | The gas | pressure |
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| switch(es) (if equipped) must close. |
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•If the contact for the louvers is closed, the louver proving, HTR: Standby
and auto reset high limit (water heater only) inputs must close. OUT: 123.8F(129)
•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.
4.After the 15 second prepurge, the blower slows down and the hot HTR: PREPURGE
surface igniter (HSI) is energized. The HSI is heated for at least OUT: 123.9F(129) 20 seconds.
5.Once the HSI is hot, the trial for ignition begins with the HTR: IGNITION
| opening of the gas valve. | OUT: 123.9F(129) |
6. | If the SMART SYSTEM control does not sense flame, then it will | HTR: POSTPURGE, LOCKOUT |
| lock out. | OUT: 123.9F(129) |
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7. | If the SMART SYSTEM control senses flame, it will fire the burner |
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| to maintain the set point. The firing rate will stage as required to | HTR: RUN STG: 1 |
| 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 | OUT: 124.8F(129) |
| active (default is disabled), the staging will be held to a series of |
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| increasing limits after the burner has lit. |
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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 HTR: DHW STG 123
2 seconds, and then turn off the boiler pump. This will divert the OUT: 177.8(180) 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.
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, HTR: RUN STG 12
and resume firing based on the space heating set point. As long OUT: 123.0F(129) 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.
10.Once both calls for | heat are satisfied, the control will turn | HTR: POSTPURGE |
off the burner. The | blower will remain on for the 30 second | |
postpurge cycle. Any pumps that are running will continue to run | OUT: 127.4F(129) | |
for their respective pump delay times, then turn off. |
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11.Boiler pump off, system pump continues its delay if longer. | HTR: Standby | |
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| OUT: 124.7F(129) |
12.System pump off. |
| HTR: Standby |
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| OUT: 122.9F(129) |
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