Gas Hot Water Heater Troubleshooting: The Best Repair Guide

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A gas hot water heater is a type of appliance that heats water using natural gas or propane.

These appliances are very common in homes because they are affordable and reliable.

They also provide hot water 24/7 without having to worry about electricity bills.

However, gas hot water heaters (see also ‘Gas Hot Water Heater Installation‘) come with some maintenance issues that homeowners should be aware of, particularly because escaping gas can be toxic and deadly.

We take a look at how your gas hot water heater (see also ‘ How To Remove Sediments From Water Heaters ‘) works, and what can go wrong with it.

How Does A Gas Hot Water Heater Work?

A gas hot water heater works by heating the water inside a tank.

The water is heated through the use of heat generated from the combustion of natural gas or propane, which is stored in an underground storage tank.

The main components of a gas hot water heater include:

Water Heater Tank

The water tank is where most of the water is kept when it’s not being used for showering or bathing. Depending on the size of the tank.


The thermostat controls the temperature of the water. The thermostat can either be manual or automatic.


The piping is a network of tubes that connects all parts of the system.

Venting System

In addition to the pipes, the system of vents is an important part of a hot water system with gas burners.

The amount of air in the gas chamber can impact the performance and efficiency of your hot water system.

If the vent is installed at the wrong angle, then this can reduce the efficiency of your heating system by up to 50%.

This is a significant loss, costing you not just valuable warmth but also cash.

We always recommend installing a vent that rises straight up, instead of an L-shape. This makes the air supply into the gas chamber most efficient.


The furnace (see also ‘Why Is My Heater Blowing Cold Air? | Furnace Troubleshooting‘) contains burners that heat the air inside the home. When this air gets into contact with the water, it creates steam.

Pressure Relief Valve

This valve prevents any excess pressure build-up within the tank. If there is too much pressure, then it will open automatically and release any excess pressure.

To work properly, a gas hot water heater (see also ‘Best Hot Water Heater For Hard Water‘) needs to have enough fuel supply. Therefore, you’ll need to check if the tank has enough fuel before starting the repair process.

Troubleshooting Gas Hot Water Heating Systems

If you notice that the water coming out of your faucet isn’t as warm as usual, or you don’t have any hot water at all, then this could have several causes.

Here is a troubleshooting guide for how to fix your gas hot water heating.


When water is heated with gas, then the flue gasses can cool down so far that they create condensation.

The moisture can then enter the gas chamber and it can impact the flame of your pilot light.

The cause of the cooling of flue gasses is often cold air and a cold flue pipe surface. This usually happens with new heaters that are filled with water for the very first time.

Condensation in the gas chamber can also be caused by large amounts of hot water being used in a very short period of time.

You will notice condensation when you spit water droplets near the heater after you use the gas water heater.

You may be able to spot water dripping, or something red, or black spots on the gas burner. Other symptoms of gas heater condensation include water gathering at the top of the heating element.

The water in itself isn’t always an issue. However, the increased moisture in the gas chamber becomes an issue when it drops onto the burner.

This does not only create an unsettling sizzling noise, but it can affect the heating output. Too much condensation can even put out the pilot light.

The best way to fix condensation after a gas hot water heating operation is to raise the air temperature of the supply.

Alternatively, you can also increase the tank size, or increase the temperature of the water stored in the tank.

Gas Smell

Another common problem when using a gas hot water heater is the presence of a strong odor (see also ‘How To Get Rid Of Water Heater Odor‘).

It can come from various sources, such as:

  • Leaking gas lines
  • A bad connection
  • Improperly installed valves
  • Dirty filters

These smells are generally harmless. However, safety comes first, so you should turn off the gas supply and let the smell dissipate naturally first.

If the problem persists, it’s best to contact a gas heating specialist as soon as possible.

The Pilot Light Is Off

If you turn off the pilot light, then you won’t get any hot water. This means that the burner is working correctly.

However, if the pilot light doesn’t work, then you may need to replace the flame sensor.

You can check whether the pilot light is on or not, by looking through the front glass below the valve.

In older units, you may have to remove a front panel to see the pilot light.

If the pilot light of your gas heater isn’t working, then check the gas supply and the gas pressure first. If you find that there is no gas supply, then contact your utility company to check the issue.

Sometimes you will find that air is trapped inside a gas line, and this can lead to the pilot line, not lighting. To release this air, a professional technician will need to bleed the gas line.

Occasionally during short gas outages, a pilot light may go off, and you will need to relight it again. This is typically done by pressing a button.

You must press the pilot lighter button firmly, and you should hear a light clicking sound. This is the electrode sparking the light.

If you cannot hear the clicking, then the igniter may not be working properly.

Gas Hot Water Heater Troubleshooting: The Best Repair Guide

You may also need to check the pilot tube which may be dirty or clogged, so it’s best to clean this.

Check the thermocouple connection to see if it is loose. This usually connects the pilot light with the gas valve.

If you find that this connection is loose, then you will need to tighten it with a wrench. The thermocouple must be tightly fitted, so it makes contact with the pilot light.

May may also notice melted ignition wire or insulation around the ignition. It’s best to replace this as soon as possible.

If you notice the pilot flame going out periodically, then this may be caused by not enough air in the combustion chamber, a clogged vent, incorrect gas supply or gas pressure, or condensation in the gas chamber.

Some modern gas valves indicate with a flashing light when there is a problem with the gas supply. You will then just need to find out about the error code.

Burner Won’t Stay Lit

If the burner doesn’t stay lit, then you’ll need to check the gas supply and gas pressure.

Make sure that the gas supply is turned on, and that the gas pressure is high enough for the burner to operate.

If the burner still won’t stay lit, there are several reasons, such as too high room temperature, obstructed vent, or clogged air intake.

If you address these issues, then you may find your burner will work again as it should.

Black Sooting

Soot build-up on the burner can cause blackening of the burners and other parts of the unit, such as the flue vent and the gas chamber.

This can happen due to high gas pressure, any of the gas fittings not being connected properly or a wrong orifice has been used.

You may also notice sooting when the main burner flame or the pilot flame is either too small or too big.

This problem can also be caused by the wrong size of tubes and orifice, so it is important to check the manufacturer’s instructions to ensure you use the right sizes.

No Hot Water

This may be one of the most common issues with gas hot water supplies. No hot water (see also ‘Hot Water Not Hot Enough: Common Problems and How to Fix Them‘) coming out of the tap means that something needs fixing.

The first thing to do is check the gas supply. Sometimes gas supplies may not notify you of smaller issues.

Gas supply issues may also be caused by other things, such as obstructions or even the main gas valve may have been closed.

If you notice your hot water suddenly going cold, then you have used up all the hot water in your tank. You will then need to wait until the heater has warmed up more water.

Unlike an electric water heater (see also ‘What To Do When A Water Heater Gets Frozen?‘) a gas water heating system relies on the pilot light being on all the time. If this isn’t burning, then you will end up with cold water.

Over time, you may notice that the hot water isn’t as warm as it used to be. If this is the case, then there may be sediment build-up in the pipes.

Faulty Thermocouples

Thermocouples are used to measure the temperature inside the boiler. They are usually made from two wires which come together at their ends.

These wires are held together by solder, but if this breaks down, then the thermocouple may not provide a correct reading.

Thermocouples can fail because of corrosion, dirt build-up, poor electrical contact, or they can simply break.

Faulty thermocouples should be replaced by professional technicians.

Lack Of Oxygen

Oxygen is needed to keep the pilot light burning. If there is no air flowing through the line, then the pilot light will go out.

You will notice that the pilot light is out, the burner flame is sooting or the room smells of gas.

There could be several reasons why there is no oxygen flow. For example, the pilot tube may be blocked by dust or debris.

It may also be that the air intake is blocked. It is recommended that you clean the air intake regularly to prevent blockages.

If the pilot light goes out, then you will need to open the gas valve and let some fresh air into the system.

If the pilot light comes back on after cleaning the air intake, then you know the problem was fixed.

Incorrect Gas Pressure

When using a gas hot water heater, you must make sure that the gas pressure is set correctly for the type of installation.

How To Avoid Problems With Your Gas Water Heater

Prevention is the best way to avoid any issues with your hot water system. To avoid problems with your gas water heater, here are some tips to help you get started.

Make sure that the gas supply lines are installed securely. Make sure that the connections are tight and don’t allow any moisture to enter the pipe.

Ensure that the gas supply lines aren’t damaged. Check them for leaks or damage.

Regularly check the thermostat settings. Ensure that the thermostat is set to the correct temperature.

Unless you know how to work with gas, you should always get a technician to check your gas heating system.

Check the manual for instructions on how to maintain your gas equipment. This will ensure that everything works properly.

Make sure that you clean the pipes and vents regularly. How this should be done is noted in your gas heater manual.

Keep the area around your gas water heater well ventilated. You should have plenty of ventilation near your gas water heater.


A gas water heater is a great choice when looking for a new appliance. However, regular maintenance and monitoring are important to ensure that your gas water heater continues working efficiently.

When troubleshooting issues with your gas water heater, it’s important to understand that you may spot some issues immediately, and you will be able to fix them quickly.

However, if you cannot find the issue and you are not a gas expert, then it’s best to call an expert to check your gas heating system.

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