The Most Common Gas Water Heater Problems (2024)

***DISCLAIMER: PLEASE REFER TO YOUR MANUFACTURER’S INSTALLATION MANUAL FOR INFORMATION REGARDING YOUR SPECIFIC MODEL. IF YOU ARE ATTEMPTING TO SERVICE YOUR OWN HEATER, PLEASE DO SO WITH CAUTION; U.S. WATER HEATING SOLUTIONS, LLC. AND ANY OTHER PARTIES MENTIONED ARE NOT RESPONSIBLE FOR ASSOCIATED LIABILITIES. THIS ARTICLE IS MEANT TO PROVIDE AN INFORMATIVE AND EDUCATIONAL SUMMARY AND DOES NOT SUPERSEDE OFFICIAL WATER HEATER REPAIRS OR MANUFACTURER INFORMATION.

Gas Water Heaters: Troubleshooting Common Problems

Gas Water Heaters: The Basics

The Most Common Gas Water Heater Problems (1)

Overview: Gas Tankless Water Heaters

Although they aren't the main focus of this article, tankless gas water heaters have many similar parts: gas valve, burner, etc. Aside from the difference in size, tankless gas water heaters heat the water using a heat exchanger.

A flow sensor will activate the burner when water reaches the minimum flow rate; the heat from the burner is then transferred to the water via the heat exchanger (a.k.a. heat exchange, a series of copper or stainless steel tubes).

Tankless units tend to operate more efficiently than tank type water heaters since they don't experience standby heat loss.

Issue 1.0 | Poor Ventilation

Issue 2.0 | No Hot Water - Pilot Light Out

Issue 3.0 | Inconsistent Hot Water

In the case of inconsistent hot water, where you get some hot water but not enough, the two most common causes are: worn temperature sensors or thermostat shanks on the gas valve and undersized water heaters. If your water heater does not produce sufficient hot water, there may be additional causes.

Undersized Water Heater

Another issue which may lead to inconsistent hot water production is having a water heater that is too small for your needs.


A tank type water heater holds warm water in the storage tank until it's needed. Once the hot water in the tank is used up, it refills with cold water and heats the new water, which can take some time (this is called the recovery rate).


A tankless water heater produces hot water on demand, meaning you’ll never have to wait for a tank to refill (permitted your hot water demand, flow rate, and usage fall within the tankless water heater's normal operating conditions). However, every fixture in the home shares the hot water. You’ll need a unit that produces enough hot water to satisfy multiple fixtures at once, depending on your needs.

Other Common Causes of Inconsistent Hot Water

Other causes of this could be a problem in the plumbing system such as a faulty shower cartridge causing hot and cold water to mix when it should, a crossover in your plumbing (i.e., cold and hot water pipes crossed into one another), or a leak elsewhere in your plumbing system.

Faulty Shower Cartridge, Faulty Faucet Cartridge

Shower and sink faucets both have a cartridge inside. There are many different types of cartridges which control different faucet outputs; some control outgoing water speed and other control the faucet's outputs. The presence of a faulty shower cartridge or faulty faucet cartridge often becomes hyper noticeable after water heater repair or replacement. This is often the result of resolving an issue within the closed plumbing system, then opening the faucet to find the water below the expected temperature due to sediment build-up or a worn cartridge. Replacing the faulty shower cartridge or faulty faucet cartridge should resolve the issue.

Plumbing Crossover

A plumbing crossover occurs when cold water pipes and crossed with hot water pipe in your plumbing system. In other words, there is hot water entering your cold water pipes and cold water entering your hot water pipes. This issue is considered a plumbing system issue and not a water heater issue because the water heater is producing hot water, but the water coming out of your fixtures does not match the temperature setting on the water heater.

Like faulty cartridges, plumbing crossovers are the most noticeable after water heater repair, replacement, or additional plumbing services. Crossovers are most common among commercial water heater clients, but our residential water heater clients also have had crossovers they discovered after replacing their water heaters and using fixtures that were previously underused. Diagnosing a plumbing crossover may require a significant time investment depending on the number of fixtures on site, size of your plumbing system, and accessibility of your pipes.

Leak in Plumbing System

A leak in your plumbing system may also contribute to inconsistent hot water production. Temperature fluctuation in your region can cause your pipes to expand or contract, leading to potential leaks.

Loose Thermocouple Connection

The thermocouple is essentially a metal sensor (usually made of copper) that is inside your water heater pilot assembly. The thermocouple is responsible for detecting whether there is a flame/if the burner assembly is lit; then it sends an electronic signal to the gas valve, communicating whether the gas valve should open or close. If there is a weak connection between the thermocouple and the gas valve, there may not be sufficient gas entering the water heater to produce the desired water temperature.

Issue 4.0 | My Water Heater is Leaking. Can It Be Fixed?

During normal use of your water heater you should not experience any type of water leak. If your water heater is leaking, whether it can be fixed depends on the location of the leak. Many homeowners mistake plumbing leaks for water heater leaks. If you are not sure whether your water heater is leaking or it's a plumbing leak, we recommend taking a picture and/or video of the leak to share with your service provider.

Issue 5.0 | Poor Water Quality

Issue 6.0 | No Incoming Gas, Gas Leak

Get Your Gas Water Heater Repaired by U.S. Water Heating Solutions

The Most Common Gas Water Heater Problems (2024)
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