A.O. Smith Water Heater HW-520

Ensure the protector switch reset button is not depressed

Remove leads from the switch and attach to test flashlight

Does the lamp light when the flashlight is turned on?

Are the protector switch contacts open?

Depress reset button on switch if water temperature is below 200°F

Does the lamp light after depressing the reset button?

Turn off the electrical power, main manual gas shutoff, and pilot valves, if applicable.

Allow boiler parts and vent to cool before disassembly.

Remove the boiler draft diverter and vent pipe running to the chimney.

Check parts and chimney for obstructions and clean as necessary.

Remove burner from boiler and other metal parts as required to clean and vacuum the heat exchanger and combustion coils.

Refer to parts list supplied with this manual for disassembly aid.

Ensure the boiler is turned off and cooled down

Verify that all necessary cleaning solutions and tools are available

Drain the existing water from the system

Inspect the drained water for contaminants and note any unusual findings

Calculate the proper percentage of cleaning solution based on system water volume

Add the calculated amount of cleaning solution to the system

Shut off electric and gas supply to the unit

Remove pressure relief valve from outlet header assembly and install drain hose assembly

Install standpipe in tee of inlet line

Pour required amount of deliming solvent into unit through standpipe

Main Burner Characteristics Check

Verify main burner characteristics

Is there any accumulation of lint or foreign material blocking air openings?

Is there good flow of combustion and ventilating air to the unit?

Turn off electrical power and close the main manual gas shutoff valve

Allow boiler parts to cool before disassembly

Remove main burner manifold assembly from boiler

Remove loose foreign material with a vacuum