6 Common Reasons Your Gas Water Heater May Not Be Working

Having hot water available whenever you need it is something most homeowners take for granted. However, when your gas water heater stops working properly, it can be frustrating and inconvenient. There are several common issues that can cause problems with your water heater. Being able to identify and address these problems can help get your hot water flowing again quickly.


A gas water heater is a fairly simple appliance that heats water using natural gas or propane as its fuel source. It consists of a storage tank, heat source, gas control valve, thermostat, exhaust vent and various safety features. While gas water heaters are typically reliable, they can develop issues over time.

When your gas water heater isn’t working properly, the most obvious symptom is a lack of hot water. You may experience no hot water at all, low water pressure, or water that never gets hot enough. The specific reasons why your water heater fails can point you to the best solution.

This article covers six of the most common causes of gas water heater problems. Understanding the likely culprits behind your water heater malfunction can help you troubleshoot the issue or know when to call a professional for repairs. With the right knowledge, you can get your hot water flowing again quickly.

1. Pilot Light Is Out

One of the most common reasons a gas water heater will stop heating water is because the pilot light goes out. The pilot light is a small flame within the water heater that ignites the gas burner. If this light is extinguished, the water heater cannot operate.

There are a few reasons why your pilot light may be off:

  • Strong drafts or winds: Gusts of air blowing across the pilot light can cause it to go out. Vents located too close to the water heater can also contribute to drafts extinguishing the flame.
  • Dust or debris: Build up of dirt, dust or other debris around the pilot light assembly can cut off the oxygen supply needed to keep the flame lit.
  • Moisture: Condensation inside the water heater near the pilot can put out the flame. This may happen if the tank or flue are too cold.
  • Old thermocouple: The thermocouple is a sensor that determines if the pilot light is lit. After several years, thermocouples can wear out and fail to keep the gas valve open.

If the pilot light is out, the first step is attempting to relight it by following the instructions on the water heater. If it continues to go out, cleaning the pilot assembly and replacing old thermocouples are good troubleshooting steps. For persistent pilot light problems, professional service may be required.

2. Thermostat Malfunction

The thermostat controls water temperature by modulating the gas valve and burner as needed. Like other components, thermostats can fail over time. Some signs of a faulty thermostat include:

  • Water temperature fluctuates or never reaches the set point
  • Heater constantly cycles on and off
  • Water is overheating

Faulty thermostats are common in older heaters. Sediment buildup on the thermostat probe can prevent accurate temperature readings. If cleaning the probe doesn’t help, replacement of the entire control valve may be necessary.

3. Gas Control Valve Failure

Malfunctions with the gas control valve are another prevalent source of operation problems. This valve opens and closes to regulate gas flow to the burner in response to signals from the thermostat. Issues with gas valves include:

  • Failure to open: If the gas valve won’t open fully, not enough gas will reach the burner to heat the water. The pilot light may stay lit, but the main burner won’t ignite.
  • ** valve stuck open:** This dangerous condition allows gas to flow to the burner nonstop with no regulation. It leads to overheating and risks fire or explosion.
  • Erratic operation: Intermittent problems may arise if the gas valve sticks partially closed or open.

Replacing faulty gas valves requires expertise to ensure gas line safety. Hiring a professional is recommended over DIY valve replacement.

4. Faulty Burners

The main burner uses the pilot light flame to ignite the gas and produce heat for warming water. Like other components, the burner can degrade over time. Signs of a faulty burner include:

  • Burner flame is orange or yellow instead of blue
  • Burner flame is uneven or only coming from certain sections
  • Burner makes popping noises when lit
  • Slow water heating

Burner problems are usually fixed by a thorough cleaning or replacement if too dirty or damaged. A technician can assess issues and service the burner correctly.

5. Sediment Buildup

Sediment buildup from hard water minerals and corrosion is a common long-term problem in water heaters. Sediment collects at the bottom of the tank and can clog many vital components like:

  • Burners
  • Thermocouple and probe
  • Gas valves
  • Dip tube

Significant sediment buildup will reduce hot water capacity. Slow hot water recovery after use is an indication of sediment fouling the tank. Flushing the water heater annually and replacing old units helps combat sediment issues.

6. Leaks

Like any household appliance, water heaters are prone to leaks from wear and tear over many years of use. Some potential leak sources on a gas water heater include:

  • Tank leaks caused by corrosion, pinholes or joint failure. Water dripping from the tank bottom is a clear sign.
  • T&P valve leaks triggered by pressure spikes. The valve releases excess water if over 20 psi.
  • Pipe connection leaks from loose, corroded or cracked fittings.
  • Heat exchanger leaks allow water to mix with combustion gases.
  • Gas line leaks which are extremely hazardous due to fire/explosion risk.

Even small leaks should be addressed quickly to prevent bigger failures. If the tank or heat exchanger is leaking, replacement is usually required. Other leaks may be repairable by a technician.

Diagnosing Problems

Determining the exact cause of your gas water heater malfunction takes a bit of troubleshooting. Here are some steps to isolate the issue:

  • Check that gas supply line is open and supplying heater.
  • Check if the pilot light is out. Attempt relighting it.
  • Inspect the main burner when heater is on. Look for proper flame or any abnormalities.
  • Verify the thermostat temperature setting is higher than water temp.
  • Test water temperature at faucets. Note any fluctuations.
  • Check for sediment buildup by draining 1-2 gallons from tank bottom.
  • Note any leaks, odd smells or noises during operation.
  • Review water heater service history and age.

When to Call a Professional

If self-troubleshooting proves ineffective at identifying or resolving the issue, contact a professional service technician. They have specialized skills and tools to fully diagnose problems and make necessary repairs. Seek professional assistance if:

  • Pilot light repeatedly goes out
  • Burners have abnormal flame or appearance
  • Temperature regulation problems persist
  • Sediment removal requires tank flushing
  • Leaks are present
  • Odd noises, smells, or errors occur
  • General troubleshooting does not reveal the cause

Proper diagnosis by a technician can pinpoint whether components like the gas valve, thermostat, burners or other parts need repair or replacement. They can also assess when a new water heater is needed.


What are the most common problems with gas water heaters?

The most prevalent gas water heater issues stem from burner/pilot assembly problems, thermostat and gas valve failures, sediment buildup, and leaks. A pilot light being out or burner problems can prevent heating. Thermostat, valve and sediment issues affect temperature regulation. Leaks signal tank or connection failures.

Why does my gas water heater pilot light keep going out?

Frequent pilot light outages usually stem from strong drafts, a dirty pilot assembly that lacks sufficient oxygen, a faulty thermocouple, or moisture buildup. Troubleshooting includes cleaning the assembly, replacing the thermocouple and protecting the pilot from drafts.

Can a bad thermostat cause gas water heater problems?

Absolutely. A faulty thermostat leads to problems like inconsistent water temperatures, failure to reach the set temperature, or constantly cycling on and off. Replacing the entire gas valve assembly generally fixes a bad thermostat.

What causes sediment buildup in a water heater?

Hard water minerals, corrosion and rust build up sediment at the tank bottom over time. Annual flushing can help minimize buildup. Older tanks more prone to corrosion accumulate more. Eventually, full replacement is needed.

How can you tell if your gas valve is bad?

Symptoms of a faulty gas valve include the pilot not staying lit, burner problems, the heater not reaching temperature, temperature fluctuations, and continuous burner operation without shutting off. Gas valves often need professional replacement to ensure safety.

Should you repair or replace an old leaking water heater?

It’s rarely worth repairing a leaking water heater more than 8-10 years old. More leaks will likely form over time. Replacement is the best long-term option to improve efficiency and reliability.


Having your gas water heater stop working correctly can be a nuisance but knowing the most common issues can help get to the root of the problem faster. The pilot light, thermostat, gas valve, burners, sediment buildup and leaks represent the majority of typical gas water heater failures. With the right knowledge of these issues, you can attempt to troubleshoot problems or know when professional service is required. If your gas heater isn’t delivering hot water properly, consult this guide to get back on track to hot showers and baths.