Gas Hot Water Heater Troubleshooting

Before you do any gas hot water heater troubleshooting and DIY repairs, one is important; leaking propane and natural gas can be dangerous. Natural gas, when it is leaking tends to rise up while propane as it is heavier than the surrounding air collects at the floor level.


If you smell a leaking gas near the gas water heater, shut off the pilot light, close the main gas valve and DO NOT activate any electrical power switch, not even light. Call plumber or gas utility immediately, from another room. This is a big problem where any spark is hazardous.

Before we show you how to do gas hot water heater troubleshooting, describe common problems and symptoms, we want you to become familiar with how gas water heater works and its main parts. To trouble shoot and do repairs is much easier after.

Gas Water Heaters, parts and how they work

  • Cold water from house plumbing enters the heater tank, through the dip tube and fills the tank from bottom up.

  • The control valve keeps the small pilot light on and once the temperature on the thermostat drops below the set temperature it ignites the burner.

  • Hot flue gases run though the flue pipe located in the middle of the tank and transfers the heat to the surrounding water, making it warmer and finally hot.

  • Hot flue gases are getting colder, because of the heat transfer and vent out either naturally or forced by power vent. Draft hood located on the top of the hot water tank provides sufficient air for proper and stable gas combustion.

  • Once you open hot water tap for shower or dishes, hot water is drawn from the top of the unit, through plumbing to the open hot water faucet.

  • TPR or temperature pressure relief valve prevents extreme pressure in the tank, helping the excessive air or water to get out.

  • For draining and tank flushing, there is a drain valve at the bottom of the tank.

  • Inside the water heater tank, sacrificial anode rod is used to prevent corrosion due to water heating process.

Now, it is much easier to do gas hot water heater troubleshooting. We will assume during this presentation that gas water heater was properly installed and was function correctly before your problem occurred.

Hot water heater problems and troubleshooting described below are related exclusively to the tank type. For water heaters troubleshooting, repairs with common problems, for both gas and electric units go back here.

Note: Basic gas and electrical knowledge are necessary for proper troubleshooting gas water heaters.

Common problems and solution

Problem #1: No hot water

Check do you still have gas in your house or to the water heater; the main gas valve might be closed. If you suddenly have no hot water, your water usage may be exceeded the tank capacity. If that is the case, wait for water heater to recover.

Another problem related to no hot water issue is that your pilot light has gone out. Relight your pilot flame according to the instructions printed on the unit. If it won't relight, you need a new thermocouple.


Problem #2: Lack of oxygen

For the proper operation of gas water heaters, fresh air needs to be delivered for gas combustion. The air should enter the gas chamber from the base of the unit and enter the flue vent from below the draft hood.

If there is an insufficient air flow, problems can rise, like: pilot outage, yellow burner flame, sooting burner flame, smell of burnt gas in the room and possible presence of carbon monoxide CO.

Solution is in prevention; check and provide enough air flow; check the flue vent and base of the water heater for possible obstructions and do not cover it with the insulation blanket.


Problem #3: Sooting

If your gas water heater is running and the chamber and flue are sooted, but the burner is clean, check is there a lack of air. If all of these elements are sooted, check: a wrong orifice might be used, excessive gas pressure, loose gas burner or loose gas connection in the burner assembly.

If pilot flame or main burner flames are too large or too small, you might have dirt in orifice or gas supply tubing, or using incorrect orifice size. Follow manual for the right spec.


emergency plumber

Problem #4: Condensation

When gas is burning, flue gas cools to the "dew point" resulting in condensation than can go back to the gas chamber.

What can cause flue gases to cool are cold air supply and cool flue pipe surface. It usually happens when a new heater is filled with cold water for the first time.

Condensation also happens if large amount of hot water is used in a short time and when the incoming water is very cold.

Another reason for condensation is the increased combustion efficiency, usually when above 87.5% of flue heat is transferred to surrounding water.

Symptoms when condensation occurs are water around the heater right after the gas water heater operation; water dripping, small black and red spots on the gas burner, top of the heater and vent piping (that is the reason for using PVC or more expensive stainless steel vent pipes).

When condensate falls onto the burner you can hear a sizzling or frying noise.

Solution is to raise the supply air temperature, stored water temperature or even tank size (make sense if the existing one is too old, and low performing).


Problem #5: Burner won't stay lit

  • High ambient room temperature

  • Dirty or clogged air intake

  • Flame arrestor openings are blocked


Problem #6: Pilot light won't light or stay lit.

Check is there a gas at all or is the gas pressure low, and if there is a problem with the gas supply, call the utility company.

If there is an air in gas line, bleed the air from the gas line (should be done by certified technician).

When attempting to light pilot, be sure that the pilot light button is fully depressed. Check is the pilot electrode sparking to pilot and is piezo igniter working properly.

There might be also a defective magnet in combination thermostat-gas valve, replace it if necessary.

If the pilot tube or orifice is clogged, clean it. If thermocouple connection is loose with gas valve or in pilot light assembly bracket, tighten it with your finger and 1/4 turn with the wrench, it might need just a simple adjustment.

Thermocouple has to be properly secured and in contact with the pilot flame. If it is broken, replace it. If you have a melted insulation on igniter wire or shorting of igniter wire replace it.


If pilot light goes out periodically, these might be the cause of the problem: condensation may be extinguishing the pilot light, insufficient combustion air supply, clogged or incorrect vent system or inconsistent gas supply and pressure.

Checking the vent system

Venting system is very important for the safe water heater operation and its efficiency. 90 degree elbow installed on the top of the tank draft hood, can reduce the vent efficiency by up to 50%. Recommendation is to install vent system that rises straight up. For horizontal vent pipes there are some different installation rules that has to be followed (use manufacturer's manual for info).

Decompression is another reason why the pilot flame will fail. If air cannot enter as fast as it is being used, the air pressure drops below the outside pressure and it creates an effect called "capping".

Solution for decompression is to make two air vents on the outside wall, one close to the ceiling and the other closed to the ground; if not and the room is on the balcony for example, provide venting opening on the door.

Note: when you do a gas hot water heater troubleshooting and repairs, make sure that gas supply is off and always refer to the user manual.

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