Lochinvar 400 - 801 service manual Operation Display

Service Manual

1Service (continued)

Table 1-1Sequence of Operation

1. Upon a call for heat, the gas pressure switch(es) must be closed.

2. Once the gas pressure switch(es) are closed, the control turns on the appropriate pumps (system and boiler pumps for space

heating, DHW pump for DHW). The flow switch and/or LWCO must close.

4.The control starts a 15 second prepurge cycle by initiating the blower.

5.The control starts a 4 second trial for ignition by firing the spark electrode and opening the gas valve.

6.If flame is not detected within 1 second after the sparking ends, the control will perform a 10 second post-purge, then start another prepurge cycle and try to light the burner again. On the 501 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.

7.If flame is detected, it holds the firing rate steady for 5 seconds to let the flame stabilize, then it begins to modulate the firing rate based on a set point or some other command (such as a 0-10V BMS signal).

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