Servicing a Water Heater

Most water heaters fail early because nobody looks after them. Sediment builds up, the anode rod wears away, and scale chokes the heat exchanger. A short service visit once a year can add years to a heater and catch a problem before it floods a building. Many of the calls you get will not be for a new heater at all. They will be for a heater that is noisy, leaking, or not making hot water. You need a routine for the service and a method for the diagnosis.

What You Will Be Able to Do

• Test a relief valve and judge the result
• Flush sediment from a tank
• Inspect an anode rod and know when to replace it
• Descale a tankless heater
• Work through a no-hot-water call and decide between repair and replacement

Before You Touch It

Three hazards come with every service call.

• Hot water: It can scald in seconds. Let the unit cool when you can, and wear gloves and eye protection.
• Electricity: Electric heaters run on 240 volts. Turn off the breaker, lock it out, and test for zero volts at the terminals before touching them.
• Gas: If you smell gas, leave and follow your emergency steps. Only qualified workers should repair gas controls.

Read the label and manual for the unit. Controls and service steps differ a lot between models.

The Yearly Service

Testing the Relief Valve

The temperature and pressure (T&P) relief valve is the heater's most important safety device. Test it about once a year.

1. Find where the discharge pipe ends, and make sure nothing and no one is in the path.
2. Lift the test lever briefly so water flows through the pipe, then let it snap back.
3. Watch the end of the pipe. Water should stop within a short time.

If nothing comes out, or if the valve keeps dripping, replace it. An old valve that has not moved in years may not reseat after a test. Warn the customer before you test it.

A valve that drips on its own usually points to pressure from thermal expansion or too high a house pressure. Check those before you replace the valve.

Flushing the Tank

Sediment settles on the bottom. On a gas unit, it insulates the tank from the burner, wastes fuel, and can overheat the steel. The water trapped under the sediment boils in small bursts, which is the popping sound people call kettling. On an electric unit, sediment can bury the lower element.

1. Turn off the gas control to pilot or the breaker.
2. Attach a hose to the drain valve and run it to a floor drain or outside.
3. Close the cold inlet and open a hot tap, or follow the manual.
4. Open the drain valve and let the tank empty.
5. Open the cold inlet in short bursts to stir up the sediment, and let it flush until the water runs clear.
6. Close the drain valve. Refill with a hot tap open until water flows steadily.
7. Restore gas or power only after the tank is full.

Old plastic drain valves may break or clog. Have a replacement ready. On a neglected tank, flushing can loosen scale and cause a drain valve to leak afterward. Discuss this with the customer before you begin. Annual flushing is a good habit. Hard water may need it more often.

Checking the Anode Rod

The anode is a metal rod that corrodes so the steel tank does not. It is called sacrificial because it gives itself up to protect the tank. Once it is gone, the tank starts to rust.

Check it every 3 to 5 years. Softened water wears out anodes faster, sometimes in half the time. You will need clearance above the heater to pull the rod. If the ceiling is low, use a link-style rod that bends. Rotten egg smell in the hot water often comes from a reaction between the anode and bacteria in the water. A different type of rod, such as aluminum-zinc or a powered anode, can help, along with treating the water.

Other Quick Checks

• Look for rust, water stains, or damp insulation around the tank and fittings.
• Check that the vent is connected and sloped correctly.
• On natural-draft units, watch for signs of exhaust spilling at the draft hood, such as soot or melted plastic parts at the top of the tank.
• Check that the burner flame is steady and blue, if you are trained to look at it.
• Check the expansion tank by tapping it. The top should sound hollow and the bottom solid-ish. A tank that sounds full from top to bottom, or leaks water at the air valve, has probably failed.
• Confirm the setting is near 120 F. Measure at a tap with a thermometer.

Faults to Flag While You Are There

A service visit is a good time to catch installation problems. You may not be there to fix them, but you should report them.

Tankless Maintenance

Scale coats the heat exchanger and cuts its efficiency. In hard water, descale about every 12 months. Softer water can go longer. Many units show an error code when scale builds up.

1. Shut off power and gas to the unit.
2. Close the water service valves.
3. Connect a small pump and hoses to the service ports, with a bucket of approved descaler or white vinegar.
4. Circulate the solution through the unit for the time in the manual, often 45 minutes to an hour.
5. Drain the solution and flush with clean water.
6. Clean the inlet water filter.
7. Open the valves, purge the air, and restore power and gas.

If a unit has no service valves, recommend adding them. Check the air intake, vent, and condensate line. A clogged condensate line can shut down a condensing unit.

Diagnosing Common Problems

Start by asking when it started and what changed.

Testing an Electric Element

An element failure is a common cause of low or no hot water on electric units. This work must be done by someone trained to test circuits.

1. Turn off the breaker and lock it. Confirm zero volts at the terminals.
2. Disconnect the element wires.
3. Set the meter to ohms and test across the element's two terminals. A good 4,500-watt, 240-volt element reads about 13 ohms. A reading of infinity means it has failed.
4. Test from each terminal to the tank. Any reading there means a short, and the element should be replaced.
5. To replace it, drain the tank below the element, use the proper wrench, and fit a new gasket.
6. Refill the tank and run a hot tap until the air clears before you restore power. An element that is not under water burns out almost at once.
7. Refill completely and purge the air before you restore power. A dry element burns out in seconds.

If the high-limit button has tripped, reset it once, then find out why it tripped. It is a safety device, so repeated trips are a warning.

Repair or Replace

Give customers the facts and let them decide. If a tank is leaking, shut off the water and fuel or power right away.

Common Mistakes

Check Your Understanding

1. An electric heater gives a short burst of hot water and then goes lukewarm. Which part do you suspect first?

A failed lower element. The upper element heats only the top of the tank, so hot water runs out quickly.

2. You pull an anode and find bare core wire for 8 inches of its length. What do you do?

Replace it. More than 6 inches of exposed wire means it is worn out.

3. A gas tank makes a popping noise when the burner is on. What is the cause and what is the fix?

Sediment on the bottom of the tank. Water trapped under it boils in small bursts. Flush the tank.

4. A customer's relief valve drips every evening after people shower. The house has a PRV. What do you check before replacing the valve?

Thermal expansion. Check static pressure and whether there is a working, properly charged expansion tank.

Key Takeaways

• Test the relief valve yearly, and replace it if it does not flow or reseat.
• Flushing removes sediment that wastes fuel and damages tanks.
• Check the anode every few years, and sooner with softened water.
• Descale tankless units about once a year in hard water.
• Verify zero volts before touching electric heater terminals, and fill the tank before restoring power.
• A leaking tank shell means replacement.