Although there are countless models of water heaters, they all tend to suffer from mostly the same problems. Becoming familiar with the most common problems will mean you can repair any water heater quickly and easily, a worthy skill to add to your repertoire.

Tank Water Heaters

Make sure to turn off a tank heater before you start any troubleshooting. For electric models, this involves switching the heater off at the service panel and then using a non-contact voltage tester to confirm there is no electrical current. For gas models, just turning the thermostat to the “off” position is enough.

Water Leaks

The most common causes of leaks are:

  • Pressure relief valve — Replace the valve to stop the leak.
  • Ball valve — Tighten the nut securing the handle.
  • Loose connection or stripped threaded nipple — If the leak originates from the top of the heater and is caused by neither of the above, a loose connection or stripped threaded needle is the likely culprit.
  • Drain valve — Make sure the valve is closed properly. If that doesn’t help, replace the valve.
  • Condensation — Switch off the heater for a few hours. If this solves the problem, lower the temperature on the thermostat.
  • Tank — A leak from the bottom that isn’t due to any of the above usually means the entire heater needs replacing.

A Lack of Hot Water

There are a few reasons why a water heater may be producing insufficient or no hot water:

  • Circuit breaker — Check if the breaker is tripped.
  • High-temperature limit — Push the high-temperature cutoff reset button.
  • Heating elements — If the above doesn’t help, test each of the heating elements by touching the screws with a tester probe.
  • Thermostat — Water that is not hot enough is often due to a low temperature on the thermostats.
  • Small tank — Ask the homeowners if their water needs have increased, as it may be that they need to upgrade to a more powerful heater.
  • Dip tube — Drain the tank and replace the dip tube.

For gas water heaters, also look at the following:

  • Pilot light — It may have gone out.
  • Thermocouple — It may need cleaning or replacing.

Too Hot Water

Some homeowners are unaware that they need to adjust their water heater thermostats in the summer to stop water from being too hot in the warm weather. If you find that the thermostats are set to the right temperature, they may be broken — use a multimeter to test them for continuity.

Slow Water Heater

An electric heater that is slower than normal usually has a problem with either the heating elements (check with a testing probe) or the thermostats (check with a multimeter).

For gas units, check the heater is set to the right gas pressure. If this doesn’t do the trick, clean the burner orifices.

Dirty Water

Dirty, rusty, or smelly water is a sign the anode rod in the heater needs changing. After doing this, flush the tank.

Noisy Water Heater

Look for leaks and check the pressure valve. If these are fine, clean the heater.

Low Flow

A drop in water pressure usually means it’s time to clean the heater. Alternatively, it may be necessary to update from ½-inch galvanizing piping to ¾-inch piping.

Pilot Light and Burner Issues

If you’re servicing a gas tank heater, you may see problems with the pilot light or burner:

  • Pilot light won’t light — This could be due to a number of issues. The homeowner’s gas utility company can usually provide a free servicing.
  • Pilot light going out — Check the thermocouple with a multimeter and confirm the gas valves are in good condition. If neither of these are the problem, unclog the vent.
  • Burner going out — While running hot water, lower and increase the temperature. If this fails, the problem lies in thermocouple, burner orifices, or vent.

Tankless Water Heaters

Both electric and gas tankless water heaters are less likely to experience issues than tank water heaters, but problems can still occur. Before troubleshooting, turn off the heater using the same methods as above.

A Lack of Hot Water

Electric tankless heaters may stop providing hot water because of a worn-out heating element. To replace the element, drain the heater, remove the cover, and disconnect the wires.

For gas tankless heaters, the problem is usually a switched-off gas valve or an obstructed vent.

Finally, just like tank heaters, tankless heaters can only provide a certain amount of hot water at once. This is more often a problem for electric heaters, which are best suited as point-of-use units and for small homes. The homeowner will need to upgrade to a larger heater or purchase a second unit.

Too Hot Water

In addition to a thermostat set too high or a broken thermostat, tankless heaters can produce water that is too hot due to a faulty temperature sensor. Use a multimeter to figure out if the sensor is broken or needs repositioning.

Shutdown Heater

When demand for water becomes too high, a heater can shut down. Just reset it.

Buildup of Minerals

To avoid mineral buildup, tankless water heaters need cleaning at least once a year (twice in areas with hard water).

Cold Water Sandwich

Unfortunately, a cold water sandwich is unfixable. Some models suffer from this problem, others don’t. This is when water comes out cold, then gives a short burst of hot water before returning to cold again.

Ignition or Flame Failure

Tankless gas heaters often show an error message if they have an ignition problem. Confirm the valves are open and, if there is one, check the gas tank has fuel.

Flame failures are usually caused by blocked venting.

Blockage in the Air Supply or Exhaust

Other problems suffered by gas tankless heaters relate to air supply and exhaust. Remove any obvious blockages and check the heater meets clearance requirements.

Whereas the majority of problems you’ll see when troubleshooting water heaters will be the above, sometimes issues are more complex. Yet other times, the water heater has simply reached the end of its life and your client needs to upgrade.

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