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A.O. SMITH
SERVICE HANDBOOK
Residential Gas and Electric
Water Heaters
Prepared by the Technical Training
Department Asland City, Tennessee
The first portion of this Service Handbook addresses service issues
associated with Residential Gas Water Heaters that are atmospherically
vented and use a thermocouple as their electrical source.
The second portion of this Handbook addresses service issues of
Residential Electric Water Heaters having one or two heating elements
and common wiring config
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK TABLE OF CONTENTS Page Page Residential Electric continued Introduction Terms......................................................... 1 C-2 Circuit..........................................21 Tools .......................................................... 2 C-2 Sequence of Operation.....
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Qualifications Tools Required: For servicing gas models: • Cross top screw driver • 3/8, 7/16, ¾ inch open end wrenches • 3/16 inch Allen wrench • 11/16 inch – 6 point – socket – for anode removal • set of marked drill bits • electrical multimeter • gas pressure gauge or monometer • water pressure gauge • thermometer • tubing cutter if pilot tube is to be replaced • hose – to drain tank • container – to measure gal
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK GENERAL SECTION SERVICE GUIDELINES MISCELLANEOUS INFORMATION Draw efficiency is the quantity of hot water available to the consumer before the outlet water temperature decreases 25 degrees F. A 40 gallon water heater will typically provide 70% (28 gallons) of this “usable” hot water. The burner or elements are allowed to operate during this test. Incoming, cold water mixes the remaining stored water below this 25 degree
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK General Section – continued % Thermal Efficiency = (GPH X 8.25 X Temp. Rise X 1.0) divided by BTU/H Input BTU Output = GPH X 8.25 X Temp. Rise X 1.0 GPH = (BTU/H Input X % Eff.) divided by (Temp. Rise X 8.25) One cubic foot of Natural Gas contains about 1000 BTU of heat. One “therm” is equal to 100,000 BTU One cubic foot of Propane Gas contains about 2500 BTU of heat. One gallon of Propane gas contains about 91,2
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK INSTALLATION OF RESIDENTIAL GAS WATER HEATER Water Exhaust Vent to Shut Off Outside of Building Valve Union Union Expansion Tank Pressurize to Equal Supply Water Pressure See Manual and Labels For Installation Clearances Temperature And Pressure Relief Typical Model Valve – Do Not and Rating Reuse Old Valve. Plate Location Temperature and pressure relief valve tube piped to within 6” Maximum Gas Supply
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK RESIDENTAL GAS WATER HEATER SERVICE This portion of this manual applies to the Operations and Servicing of Residential Gas, Tank Type, Water Heaters, which are vented atmospherically and use a thermocouple as their electrical source. Construction: See also “General” section of this manual. Control: There is one control on this style of water heater. The control has a main gas regulator, pilot gas regulator
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas – continued Burner: The burner assembly consists of the main burner, main burner orifice, main burner gas supply tube, pilot burner, pilot burner orifice, pilot burner gas supply tube and thermocouple. The pilot burner remains on once it is manually lit. When incoming cold water activates the thermostat, gas flows to the main burner. The pilot flame ignites this gas. The main flame burns until the tank re
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas – continued Temperature: Two metal probes mounted onto the back of the control are immersed inside the tank water. One probe (the shorter) acts as a temperature high limit. If water gets excessively hot, a sensor within the probe opens, interrupts the small electrical current to the gas valve, and gas flow through the control is interrupted. If this safety sensor opens, the entire control must be repla
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas - continued Water Flow: When a hot water faucet is opened, water pressure from the well tank or street main forces cold water into the water heater. This pushes hot water out of the tank. Operation: A residential water heater is not a precise operating appliance. Because the water heater relies on the expansion and contraction of a metal rod, when the thermostat dial is set at an indicated setting (“▲ ” is re
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas - continued Service: Air: A gas burning appliance requires the oxygen contained in 12.5 cubic feet of air (at sea level) for every 1000 BTU of heat that is generated. If your water heater has a BTU per hour input of 40,000 BTU then a minimum of 500 (40 times 12.5) cubic feet of clean air must be available. This oxygen will mix with the gas for a clean, blue flame in the burner chamber and provide dilution ai
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas – continued The instruction manual gives guidelines under “Air Requirements” and “Unconfined “ or “Confined Space” sections. If you want to test for a lack of air: 1. Turn on every appliance and fan that exhausts air from the utility room and/or house. Make sure all windows and doors are closed, as well as chimney dampers. 2. Open a hot water faucet so that the main burner will ignite 3. Remove the outer doo
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas - continued Sooting causes: If … … then the burner is clean but the chamber and/or flue check for lack of supply air. are sooted the main burner, chamber and flue are sooted check the following: • incorrect orifice • excessive gas pressure • loose main burner • cross threaded orifice • gas control valve gas seepage • loose gas connection in burner assembly. Electrical Testing This type of water
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas - continued Electrical Testing– continued Millivolt dropout test through copper magnet winding and ECO (Emergency Cut Off) Procedure: Move meter probe to upper ECO solder joint and ground If … … then reading of at least 10 MV is not present replace the control valve. reading of more than 10 MV is present but, replace the control valve. gas to the pilot shuts off each time knob is released Safety drop o
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas – continued Condensation is a mild acid – it will corrode steel Condensation is usually noted when: • water dripping is heard (only) while the main burner is on, • there is “water” around the heater just after the heater has been operating, • there are small, black or red granules on the main burner or top of the heater or • corroded jacket or vent piping is noted. If … … then any of the above cond
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Gas – continued Exhaust Venting Notes Follow current National Fuel Gas Code requirements for proper installation. “D” – Typically, same or larger diameter as Draft Hood outlet “L” – Horizontal piping slopes upward ¼” per foot from heater to chimney or vertical vent Length of horizontal not more than 75% of “H” “H” – Not less than 5 feet Maximize vertical distance to first elbow
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK STANDARD RESIDENTIAL ELECTRIC WATER HEATERS INSTALLATION SOME MODELS MAY HAVE SIDE OR REAR CONNECTIONS COLD WATER TO †FUSED INLET LINE ELECTRICAL TEMPERATURE AND SUPPLY PRESSURE RELIEF VALVE (BREAKER BOX) OPENING MAY BE ON SIDE OR TOP OF HEATER. DO SHUTOFF UNION NOT REUSE OLD VALVE VALVE †FUSE SHOULD BE RATED UNION AT AMPERAGE INDICATED HOT WATER ON RATING PLATE TIMES TO FIXTURES 125% ELECTRICAL JUNCTION
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK STANDARD RESIDENTIAL ELECTRIC WATER HEATERS This portion of this manual applies to the Operation and Servicing of Residential Electric, Tank Type, Water Heaters. The illustrations are for two element models but the information also applies to single element models. Multiple Heater Water Piping Required for Proper Operation of Top Connect Models TEMPERATURE/PRESSURE RELI
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK STANDARD RESIDENTIAL ELECTRIC WATER HEATER SERVICE GUIDELINES Construction See “General Section” for features common to both gas and electric models. Miscellaneous: Amperage (Amps) (1 phase) = Watts divided by Volts Amperage (3 phase) = (Watts X .577) divided by Volts KW Required = (GPH X 8.25 X Temp. Rise X 1.0) divided by (3413) Ohms = Volts divided by Amperes One kilowatt is equal to 1000 watts One k
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RESIDENTIAL GAS AND ELECTRIC WATER HEATER SERVICE HANDBOOK Residential Electric – continued Since the element (s) are - very nearly - totally immersed in the tank, thermal efficiency is assumed to be 100%. – all of the Btu (Watts) generated, enter the water. B. A. C. • Watt Density = the density of the wattage output of the element compared to the surface area of the element (i.e. “High Watt Density Element” will have the most wattage per square inch of element surface. If the abo
