Test for carbon monoxide emissions.

Check all gas connections and components for gas leaks.

Measure and ensure pressure and temperature readings are within the appropriate ranges.

Look for any service codes or errors on the display panel.

Check the flue gas vent piping and combustion air piping for any signs of leakage, corrosion, or deterioration.

Ensure all joint and pipe connections are tight.

Inspect the condensate drain system (drain line, PVC fittings and drain trap) for blockages.

Ensure air inlet and vent terminations are clear and unobstructed.

Check to ensure the combustion air opening is unobstructed.

Check for any unusual noises or vibrations.

Inspect the boiler relief valve and discharge pipe for signs of weeping or leakage.

Examine high-limit switch, zone-valve, and mixing-valve performance.

Have low water cutoff tested.

Inspect and clean heat exchanger.

Inspect, clean and flush condensate system.

Inspect and clean burner assembly (including ignitor and flame sensor).

Adjust burners (if necessary).

Ensure all wiring and cables have stable connections, and replace loose and worn wires.

Check water PH levels.

Check control settings and test safety-controls.

Ensure boiler is operating at peak performance after it has been cleaned and inspected.

Ensure proper functioning of water regulator.

Examine expansion tank.

Examine ignition and thermocouple.

Perform air-flashing on the system.

Measure gas manifold pressure.

Inspect safety limit switches.