Gas Water Heater Troubleshooting Guide

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A guide for gas water heater troubleshooting. The most common problems; symptoms and causes. Troubleshooting low performance, insufficient hot water, pilot light problems, improper gas combustion...

Gas hot water heater troubleshooting guide will assume that the unit has been correctly sized, professionally installed, per codes and manufacturers' instructions. The problems such as leaking, smelly water, noise, corrosion and other, similar to the problems found in electric units are described here.

Note: before calling the plumber or the licensed HVAC technician for the problems related to your gas water heating, recommendation is to read the gas water heater troubleshooting guide found here, and the instructions from the manufacturer manual (if you still have one).

Combustion odor and sooting

Smoking and carbon formation and the combustion odor are water heater problems that are very dangerous for its owners, if not resolved. This is why the gas water troubleshooting article puts these problems at the top of the list. Such problems should be troubleshoot and treated with caution.

  • If you find smoking and carbon deposits and smell the burning gas inside your home or room where the gas water heater is installed this is what you should check: check for any obstruction in the vents, flue baffle and burner. The venting path should be clean of any dirt, dust and deposits. Preventive inspection and maintenance can reduce the cause.
  • An insufficient fresh air supply, which can happen in the confined spaces, is another major cause of the sooting and combustion odor. Properly sized openings on the outside wall for the fresh air intake is one of the solutions. Manufacturer usually recommends the size of the openings, and how much air is needed for the proper combustion.
  • Your gas unit might be receiving the excessive gas pressure.
  • Tighten the main burner or gas connection if loose.
  • Replace the orifice if the unit is using an incorrect size.

Troubleshooting gas hot water heaters - Burner does not ignite

  • The main burner won't ignite because of the pilot light problems - this problem will be described below.
  • If the main gas burner line is clogged, there is a dirt in the gas line, or pilot line, make sure to clean it all.
  • Replace the thermostat and thermocouple if you find them broken.
  • For gas water heaters installed in the confined areas, make sure to provide a good venting with sufficient air supply.
  • Bleed the air from the gas line.
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Pilot light assembly problems

  • Check is the igniter working properly and generates sparks.
  • Problems with the thermocouple. If the thermocouple is broken, replace it. If it is misaligned, position it properly. Tighten the loose connections.
  • Is the venting correct? Lack of the fresh air will cause the pilot light outage.
  • Check are the flame arrestor and filter clean of lint, dust and dirt.
  • Replace the thermostat if it is broken or ECO switch is open.
Find more details about troubleshooting pilot light problems here.

Insufficient hot water and slow recovery

  • Insulate the pipes if they are exposed to cold weather and are lengthy.
  • Check the flue vents for the blockage to see is there an insufficient air supply. Clean the vents and flue baffle if needed.
  • Check the thermostat and if it is calibrated improperly, replace it.

Problems with the burner flame

  • If the burner flame floats, lifts off the ports, or is too large, you might have an incorrectly installed burner orifice (too large) or the vent system is blocked.
  • For the yellow lazy flame, clean the dirt from the burner gas supply line, clean the orifice, vent system and provide sufficient fresh air to the water heater.

How to troubleshoot condensation in gas water heaters

There are three, the most common causes of the condensation problem on gas tank water heaters:

  • A new gas water heater is filled with the cold water and runs for the first time.
  • Great amount of hot water is used in short period of time, and the tank is refilled with the cold water. This is common on undersized gas water heaters.
  • Most of the today's heaters are energy efficient, high efficient or Energy Star water heaters, and since they work with the lower temperatures of the flue gases, condensation forms more often. Good venting is very important to carry away the flue gases and water vapor safely.

Keep also in mind that the flue gases contain a large amount of water vapor, which is by its nature acidic. The acidic condensate can affect the metal surface by corroding it. It can usually be seen around the draft hood.

Condensate problem should be eliminated or at least reduced, as the excessive condensation can cause the pilot light outage, sizzling noise on the burner and puddle of water under the unit.

One of the simplest solutions for the water heater condensation is to increase the temperature settings, if the temperature is too low.


Gas water heater troubleshooting guide is not for one specific brand or model; it covers Rheem, AO Smith, Bradford White, State, GE, Kenmore, American and other manufacturers. If you find problems, which are not presented in this troubleshooting guide, and you cannot solve them, it is recommended to call a licensed technician. If looking for the replacement parts use the genuine elements or from the trusted name, with the same characteristics and per manufacturer's specs.

Regular maintenance and clean heater's environment should be the first thing to consider when troubleshooting a gas water heater.

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