The light is telling you that the temp has dropped to the point that it needs the fire lit to heat the water. The red light should come on and then go out once it gets hot and stops calling for heat.
If it is flickering, it is trying to light; and failing for some reason.
The fact that it lights after 1 or 2 tries, means that the mixture is not optimum.
My money is on a bugs nest in the venturi tube.
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