9
Table 1A Sequence of operation
1 Service (continued)
Service Manual
1.
Upon a call for heat, the control turns on the DHW pump.
2.
The control confirms that the low water cutoff / flow switch contacts are closed and energizes the louvers (optional).
3.
The control confirms that the gas pressure switch, blocked drain switch, limits, louver proving switch (optional), and
contacts close. The Pre-Purge cycle begins.
4.
The control confirms the blower comes up to the desired speed.
5.
Once the Pre-Purge cycle is complete, the control lowers the blower speeds, initiates sparking of the ignition
electrode, and opens the gas valve.
6.
After a short wait, the control stops sparking and checks for the presence of flame current through the flame sense
electrode.
7.
If the  ame is not detected a er the sparking ends, the control will perform a postpurge, then start another prepurge
cycle and try to light the burner again. On the 500 and larger models, the control will lock out if this second attempt
also fails. On the 400 model, the control will perform a total of 4 attempts before locking out. Once the control has
locked the unit out, the RESET button will need to be pressed on the touch screen LCD.
8.
If the control detects flame current, the control will hold the blower speed constant for a few seconds to allow the
flame to stabilize, then begin modulating the firing rate in order to maintain the controlling sensor to the desired set
point temperature.
9.
Once the DHW call for heat is satisfied, the control will turn off the gas valve and begin the Post-Purge cycle. Any
pumps that are running will begin their respective Pump Delay cycles.
10.
At the end of the Post-Purge cycle, the louver relay contacts will de-energize.
11.
At the end of the Pump Delay cycle(s), the pump(s) will be turned off.
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