Fujitsu Waterstage DHW Series Operating Instructions Manual page 21

LED Off:
The circulation pump is not working, no power supply .
Green LED On:
The circulation pump is operating normally .
Green LED flashing:
Venting mode in operation (10 minutes) .
Red/green LED flashing:
Operating error with automatic restart .
Red LED flashing:
Operating error, consult your heating engineer .
fig. 12 - Operating signals of the HP circulation pump
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Waterstage / OPERATING INSTRUCTIONS / 2010 - EN