Diagnosing Common Water Heater Issues


It’s never fun when you have an essential part of your home stop working, and water heaters are no different. While there are many different models available on the market today, for the most part, they all function the same and as a result, can be prone to the same issues and problems. Knowing what issue your water heater is having keeping it from heating your water, as well as how to fix said issue(s) will help you in repairing the unit. For many common water heater problems, you will be able to fix them yourself. However, for some more serious issues, you will need to hire a qualified plumber to repair or replace the unit.

Tank Water Heaters

Before you begin to diagnose what is wrong with your water heater, you will want to make sure to turn it off beforehand. For electric water heaters, you will need to turn the unit off at the service panel and use a voltage tester to double-check that it is not running; for gas units, simply turn the thermostat to the off position.

Water Leaks

Generally, a water heater will leak due to a few different reasons:

Pressure Relief Valve

To halt the leak and take care of the issue, you will simply need to replace the water relief valve

Ball Valve

Make sure that the fittings are tight, especially the nut that secures the handle

Loose Connection or Stripped Threading

If the source of the leak is the top of the heater then you can rule out the above reasons and should instead look for a loose connection or stripped threading.

Drain Valve

Ensure that the valve is properly closed; if it is, then try to replace the valve.


Turn off the water heater for a while, and if there is no leak after a few hours, the water you see is due to condensation and turning down the temperature on the heater should solve the issue.


Unfortunately, if you notice a leak at the bottom of the tank, then this generally means that the whole unit will need to be replaced.

Lack of Hot Water

There are a few indications and reasons why your water heater may be not producing adequate hot water if any at all:

Circuit Breaker

Make sure that power is flowing to the water heater, and check the circuit breaker to double-check

High-Temperature Limit

Reset the high-temperature settings by hitting the “reset” button

Heating Elements

By using a tester probe, you can check the screws on the heating elements to make sure they are functioning properly.


If there is hot or warm water, but it is not hot enough, that could be an indicator that the thermostat will need to be adjusted.

Small Tank

If you find yourself running out of hot water frequently, it may be time to upgrade the tank size.

Dip Tube

Replace the dip tube (remember to drain the tank first).

Pilot Light

Make sure that the pilot light remains lit.


May need to be replaced or cleaned.

Water is Too Hot

One thing that not a lot of people realize is that during warmer summer months, you will want to adjust the thermostat on your water heater as it will naturally be hotter during this time. However, if you feel like the thermostat is significantly too hot, then you may want to use a multimeter to test it to make sure that it is functioning properly.

woman lifting his leg

Water Heats up Slowly

If you notice that your electric water heater is taking a long time to heat water, then you may want to double-check the heating elements and the thermostat(s) are working properly.

For gas heaters, either clean the burner or make sure that the heater is set to the correct gas pressure.

Dirty Water

If you notice that your water is dirty, has the color of rust, or has a foul odor then you will want to change the anode rod in the heater; after performing this action, make sure to flush the tank.

Noisy Water Heater

Check the water heater for leaks and double-check the pressure valve; if both are fine, then try to clean the heater.

Low Water Flow

This is an indicator that it is time to clean the heater, and once completed the water flow should return to normal.

Pilot Light and Buner Issues

This section only pertains to gas water heaters, as electric ones do not have pilot lights.

Pilot Light Won’t Light

Although there are various reasons why the pilot light won’t light or stay lit, a visit from your gas company can generally diagnose the reason why.

Pilot Light Not Staying Lit

For this issue, you will want to double-check the thermocouple by using a multimeter just to make sure that the gas valves are in good working condition.

Burner Going Out

While running hot water, lower and increase the temperature to diagnose. If this does not work, then the issue is with the thermocouple, burner, orifices, or the vent.

Tankless Water Heaters

While both gas and electric water heaters are less prone to issues than tankless ones, issues can still occur. Before beginning to diagnose and attempt to fix the problem, make sure to turn off the heater and use the above methods.

A Lack of Hot Water

If you have a heating element that is old and not working properly, electric tankless heaters may not provide hot water. To replace the heating element, drain the heater and remove the cover before disconnecting the wires.

For gas tankless heaters, the problem generally lies with a turned-off gas valve or an obstructed vent.

It is important to note that similar to tank heaters, tankless water heaters are only capable of providing a limited amount of hot water at a time. Electric water heaters are more prone to this, which are better suited for smaller single-family homes.

water from round gray stainless steel shower head

Water is Too Hot

Much like water heaters with a tank, tankless ones can provide water that is too hot due to a malfunctioning thermostat, or a faulty temperature sensor. By using a multimeter, you can diagnose this issue to determine if the sensor is broken.

Shutdown Heater

If your household demands are too taxing for your water heater, it may occasionally shut down; simply reset it.

Mineral Buildup

To avoid mineral buildup in your water heater, it is recommended to clean it at least once a year; twice if you have hard water.

Cold Water Sandwich

This term refers to when the water comes out cold, with hot bursts before returning to cold again. Unfortunately, there is no resolution for this and some models are prone to this, while others are not.

Ignition or Flame Failure

If there is an ignition problem in your tankless water heater, generally there will be an error message. For this, make sure that the unit has gas and that the valves are all open.

Blockage of Air Supply or Exhaust

Lastly, some issues with tankless water heaters are due to lack of air supply or no proper exhaust. Remove anything that may be obstructive, and check that the heater is in the right location for clearance.

Although many of the issues that you will face with water heaters are listed above, some are more complex or have a combination of reasons. Additionally, sometimes water heaters are just old enough to give out and will need to be replaced.

About RJ Frometa

Head Honcho, Editor in Chief and writer here on VENTS. I don't like walking on the beach, but I love playing the guitar and geeking out about music. I am also a movie maniac and 6 hours sleeper.

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