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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, blocked drain
switch, 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 10 second prepurge, the blower slows down and the hot surface
igniter (HSI) is energized. The HSI is heated for at least 15 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 within 7 seconds of
the opening of the gas valve, then it will lock out.
HTR: POSTPURGE, LOCKOUT
OUT: 123.9F(129)
7. If the SMART SYSTEM control senses flame within 7 seconds, it will fire
the burner to maintain the set point. On B9 and M9 models, the firing rate
will modulate 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 modulation will be held to a
series of increasing limits after the burner has lit.
HTR: SH 20% RATE
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
modulate (B9 and M9 models only) to maintain the outlet temperature to
the DHW boiler set point.
HTR: DHW 85% RATE
OUT: 177.8(180)
9. If the DHW thermostat remains on 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: SH 41% RATE
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
8 Operating information (continued)
Installation & Operation Manual