Originally Posted by B47
I was told it stands for "DSI.FAULT". The red light illuminates if the DSI does not ignite the WH gas after three attempts as previously mentioned.
That is true and some installations actually label the light "Fault"; but it is more than that. It lets you know that 12 volt power is going to the control board, the unit is calling for heat, and the flame has not started yet. It does not say "it won't"; just that it has not.
In fact, even with the water hot, that light will illuminate by itself when the water cools to the low point thermostat and calls for heat. Once the flame lights it will go out by itself.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW