A. General Information
Most water heaters are fueled by either gas or electricity, but gas models are most common. Hot water leaves the tank through the hot water outlet and cold water enters through the dip tube. As the water temperature drops, the thermostat opens the gas valve, and the pilot flame lights the gas burner. Exhaust gases are vented through the flue. The thermocouple protects against gas leaks by shutting off the gas if the pilot flame goes out. The anode rod creates a reverse electron flow, which prevents pinholes from developing in the tank lining. The pressure-relief valve guards the tank against rupture from steam buildup. When a water heater leaks, immediately replace it because the inner tank has rusted through and if it gives way, the flood of scalding hot water could cause serious injury and property damage.
B. Maintenance
You can follow these steps to get longer life from your water heater:
1) Lower the thermostat to 120 degrees Fahrenheit. Lower temperatures minimize tank damage from overheating and reduce energy consumption. 2) Once a year, test the pressure-relief valve.
Lift up on the lever and let it snap back. The valve should let out a burst of water into the drain pipe. If it doesn't, install a new valve. 3) Once a year, flush the water heater by draining several gallons of water from the tank. This annual flushing removes the sediment that can cause corrosion and reduce efficiency.
C. Replace old water heater
When you buy a new water heater, remember that pressure-relief valves usually have to be bought separately. Make sure you buy a valve that matches the working pressure rating of the tank you buy.
Shut off the gas by turning the handle of the in-line valve until it's perpendicular to the gas line. Wait 10 minutes for the gas to dissipate. Shut off the water supply at the shutoff valves. Disconnect the gas line at the union fitting or at the flare fitting below the shutoff valve, using pipe wrenches. Disassemble the pipes and fittings and set them aside to use later.
Open the hose bib on the side of the tank to empty the tank.
Drain the water into buckets or attach a hose and run it to a floor drain.
Disconnect the hot and cold water pipes above the water heater. If the pipes are soldered copper, use a hacksaw or tubing cutter to cut through them, just below the shutoff valves. It's important to make straight cuts so the fittings will be watertight when you connect the new water heater.
Disconnect the exhaust duct by removing the sheetmetal screws. Remove the old water heater with an appliance dolly.
Use the appliance dolly to put the new water heater in place, positioning it so the control box is close to the gas line. Keep 6" or more clearance around the unit for ventilation, and make sure the access panel for the burner chamber isn't obstructed. Check the side of the tank with a level. If you need to, place wood shims under the legs to level the unit.
Position the flue hat so its legs fit into the slots on the water heater, then slip the exhaust duct onto the flue hat. Using a level, check the horizontal duct for the proper slope - it should slope upward ¼" per foot to keep fumes from backing up into the house. Attach the flue hat to the exhaust duct, driving #4 gauge 3/8" sheetmetal screws every 4" around the duct.
Wrap the threads of a new pressure-relief valve with Teflon tape. Use a pipe wrench to screw the valve into the tank opening. Measure the distance between the pressure-relief valve and the floor. Cut a length of copper or CPVC drain pipe that will reach to within 3" of the floor. Attach the pipe to the pressure-relief valve, using a threaded male adapter. Solder a threaded male adapter to each of the water supply pipes.
Let the pipes cool, then wrap Teflon tape around the threads of the adapters.
Wrap Teflon tape around the threads of two heat-saver nipples. If you look closely, the nipples are color coded and have directional arrows to help you install them correctly. Attach the blue-coded nipple fitting to the cold water inlet and the red-coded fitting to the hot water outlet, using a pipe wrench. Install the cold water nipple with the water direction arrow facing down; install the hot water nipple with the arrow facing up. Connect the water supply pipes to the heat-saver nipples with flexible water connectors. Tighten the fittings, using an adjustable wrench or channel-type pliers.
Gather the gas pipes and fittings that you removed from the old water heater, and test-fit them for the new unit. You might need one or two new black-iron nipples if the new water heater is taller or shorter than the old one. The capped nipple, called a drip leg, protects the gas burner by catching dirt particles. Always use black iron, not galvanized iron, for gas lines. Clean the pipe threads with a small wire brush, then coat them with pipe joint compound. Assemble the gas line fittings in the following order: 1) control box nipple, 2) T-fitting, 3) vertical nipple, 4) union fitting, 5) vertical nipple, 6) cap. Black iron is fitted with the same methods used for galvanized iron. If the gas line is made of flexible copper, use a flare fitting to connect the gas line to the water heater. Remember to use the right techniques for flare fittings.
To restore the water supply, open the hot water taps at faucets throughout the house, then open the water heater inlet and outlet shutoff valves. When the water runs steadily from all the faucets, close them. Open the in-line valve on the gas line. To test for leaks, dab soapy water on each joint. If the fittings leak, the water will bubble noticeably. Use a pipe wrench to tighten any leaking joints. Turn the gas cock on top of the control box to the PILOT position. Set the temperature control on the front of the box to the desired temperature, between 120 degrees and 125 degrees Fahrenheit.
Remove the outer and inner access panels covering the burner chamber. Light a match, and hold the flame next to the end of the pilot gas tube inside the burner chamber. While holding the match next to the end of the pilot gas tube, press the reset button on top of the control box. When the pilot flame lights, continue to hold the reset button for one minute. Turn the gas cock to the ON position, and reattach the inner and outer access panels.
