Paloma model#ph28rofp?

When water is in demand the burner will light then go out, light again & burn for approx 3-5 seconds go out even though water is still in demand will not light again or remain burning. The red led on circuit board starts blinking. The unit has a 3/4" gas supply line from the LPG tank which is 85% full. We just went through a real cold spell that froze a lot of the exterior faucets. In cleaning the water screen filter I noticed that the water did not stop all of the water from the unit. The shut off is a ball valve just underneath the unit on the out side of the house. Is it possible that a bleed back could cause this due to the faulty ball valve? Water pressure is at 115 psi in the entire house. Hopefully this problem is fixable without replacing the whole unit. Any ideas will be appreciated.