Neutralizer stone 1 Gas Hot Water Tankless Boiler: Navien Combi Boiler- Perform a tune-up and cleaning to help ensure reliable and safe operation. Inspect for cracks & deterioration of Heat Exchanger Check and clean heat exchanger- ok, Check and clean flame sensor/flame rod and ignition Assembly-ok Spark igniter. Clean Fresh air intake screen. Flush and clean condensate drain. Clean and replace Neutralizer kit, Replace Nuetralizer stones. Check Safety Controls-ok Check electrical wiring and components-ok Check Gas valve & Gas Line-ok Check Combustion Air & Exhaust-ok Check Temperatures & Water pressure settings; 19.4psi Performance-ok Check and run Thermostats- operating well at this time. Check zoning operation-isolate and run zoning. Check circulator pumps-ok amps and voltage check. Check water feeder, low water cut off, and expansion tank. Check for water leak no leakage at this moment. Run and monitored for good operations. All zones are fine supply and return lines getting hot.