Upon arrival inspected boiler. Bypassed terminal to have boiler fire. Boiler would not turn on to run. Navien combi boiler, needed to break down boiler to access flame sensor flame rod. Needed to remove inducer motor and electrical wiring connections. Inspect flame sensor. A lot of carbon build up on flame sensor flame rod. Flame sensor is corroding away. Recommending replacing. Clean flame sensor flame rod. Re-installed flame rod. Remove and clean intake air screen. Inspect gas valve and wiring components. Inspect boiler piping. Notice water leak inside cabinet of boiler and corroded piping @ boiler. Ran and test boiler operation after cleaning of flame rod. Boiler fired. On/ running. Monitor operation. Informed customer that circulator pump is running close to over amping. Factory is rated for .74 Circulator pumps range from .70-.73amps. System is back to normal operation @ this time. System could fail at anytime based on conditions of boiler. Recommended to customer to have project