Rinnai rl75i throwing code 10 repeatedly Checked concentric vent system and found no problems, took apart vent and inspected. Checked and replaced owner supplied inlet water filter Cleaned both flame rods and igniter rod and reinstalled Found massive amounts of air in hot recirculating system and on hot side plumbing upstairs. Flushed air from system and heater stopped throwing codes. Heater working now Customer stated the heater was just flushed out and that’s when it started acting up System was not properly flushed after service