Service Manual
1Service (continued)
Sequence of operation
Table 1A Sequence of operation - space heating and DHW
OPERATION | DISPLAY | |||
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1. Upon a call for heat, the control turns on the appropriate pumps | BLR: Standby | |||
(system and boiler pumps for space heating call; DHW pump | OUT: 123.8F(129) | |||
for DHW call). |
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2. The control connects 120 vac to the blower. The blower does |
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not run at this time. |
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• If the unit is equipped with a flow switch or low water cutoff, it |
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must close before the control powers up the blower. |
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• If the unit is equipped with a manual reset high limit it must be | BLR: Standby | |||
closed before the control powers up the blower. | ||||
• If the unit is equipped with a solenoid valve and/or a vent | ||||
valve, they will be energized along with the blower. | OUT: 123.8F(129) | |||
• If the unit is equipped with a gas pressure switch, it must close |
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at this time. |
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• If there is an auxiliary device connected to the unit, the unit |
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will then provide 24 vac to its enable relay. If the auxiliary |
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device has a proving switch, it must close before the |
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sequence continues. |
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3. The control then starts a 10 second prepurge cycle. | BLR: PREPURGE | |||
| OUT: 123.9F(129) | |||
4. Once the prepurge cycle is complete, and the blocked drain | BLR: IGNITION | |||
switch and | ||||
the 5 second trial for ignition by sending spark voltage to the | OUT: 123.9F(129) | |||
spark electrode and opening the gas valve. |
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5. If the control does not detect flame by the end of the trial for | BLR: POSTPURGE, PREPURGE | |||
ignition, the control performs a 10 second postpurge, another | ||||
prepurge and tries to light the burner again. If the burner does | OUT: 123.9F(129) | |||
not light after 4 trials, the control locks out for 1 hour and then |
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tries another set of 4 trials. |
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6. If the control detects a flame before the trial for ignition ends, it | BLR: SH 20% RATE | |||
begins to modulate the burner in order to maintain the set point. | ||||
If the boiler lights due to a space heating call for heat, and the | ||||
ramp delay function is active (default is off), the modulation | OUT: 124.8F(129) | |||
will be held to a series of increasing limits after the burner has |
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lit. |
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7. If the space heating call for heat is active, and the DHW | BLR: DHW 85% RATE | |||
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 | OUT: 177.8(180) | |||
DHW tank instead. The control will then modulate to maintain |
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the outlet temperature to the DHW boiler set point. |
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| 11 |
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