Water Heater Repair Tutorial: Tank and Gas Control Issues

In the second article in this four-part series, the author takes a more detailed look at troubleshooting tips to determine if the root problem resides with the water tank or the gas controls

Interested in Residential Plumbing?

Get Residential Plumbing articles, news and videos right in your inbox! Sign up now.

Residential Plumbing + Get Alerts

One of the most basic skills a plumber should have is repairing a tank-type water heater.

In the first article I looked at initial troubleshooting steps to take. In this article I will cover the specifics of how to test both kinds of potential issues — the water tank itself or the gas controls — along with real numbers to follow to successfully diagnose this type of unit.

The Dip Tube

The most common complaint when dealing with a dip tube is not enough hot water. If a customer says, “It just seems like there’s not enough hot water,” you can follow up by asking if they have been running out more and more quickly over the past few years. This is a good indication of a dip tube problem or corrosion buildup on the bottom of the tank.

In order to physically see the dip tube, you can try to take it out. Even though you will find many people telling you to just screw it out and replace it, it is usually risky to do so. The dip tube on many newer water heaters doubles as the anode rod. If the anode rod/dip tube is corroded near the top of the tank, it could break/spin out and put you in the re-tap or new water heater zone. 

One pro tip I picked up over the years is to insert a 5/8-inch carriage bolt with a head that won’t slide down inside the pipe. When the carriage bolt is inserted, it will not allow the nipple room to collapse. 

High Gas Bill

After you check everything else out, clocked the meter, etc., and you know for sure the water heater is the culprit, there are a few things to check.

First, check the house fixtures to see if hot water is leaking somewhere. If hot water is leaking out of a faucet, the gas bill will go up because it has to heat more water. The other obvious check is to verify that the gas line isn’t leaking somewhere.

Other than that you have two tracks — either something is very dirty or you are losing heat somewhere. The inside of the tank could have so much buildup that it has to heat up all that crud before it can heat up the water. The flue could be plugged, the orifice could be dirty, the burner could be dirty, etc. On the other end you could be losing heat somewhere. Take a look around. Is there a bunch of cold fresh air coming into the basement stealing all the heat from the water heater? Is there cold air drafting somewhere with a bunch of exposed uninsulated piping? In a last ditch effort, remove the circulating pump if there is one and see if that fixes it.

Combustion and Control Issues

The single most important factor is the gas pressure. Older water heaters had a lot more wiggle room as far as operational gas pressure, whereas the newer units are more precise. Accuracy and combustion are the key to a safe and reliable operation.

So what is the gas pressure? Nearly every step of the gas control diagnostic comes down to the assumption that you have the correct gas pressure. Read the sticker on the unit that will state what gas pressure the unit requires and what the acceptable range of variance is. To test the gas pressure on this type of control you need to set the gas control knob to the “off” position. Once it is off, remove the 1/8-inch plug on the gas valve and place your manometer hose in its place. Now turn that gas back on, fire up the unit and observe the gas pressure. If the gas pressure is within the allowable range, then move on to the next step. If it’s not, then what’s the problem? Is the gas pressure too high? Is it too low? Does it dance around?

Since the new burners require ultra-accurate pressures, and the gas companies are issuing fluctuating gas pressures on high-low and medium pressure systems, we need a gas regulator before the water heater to maintain a certain level of gas pressure for efficient combustion. We don’t need to necessarily stop right now in the diagnostic process and install one, but we do eventually need to install one. If you get too low of a pressure at the gas valve, then you need to shut the gas off and hook up your manometer to the gas piping itself (without going through the gas valve). If you still have low gas pressure, check the gas pressure at the gas meter. Shut the gas meter valve off before the test port, remove the test port and check the gas pressure there. If you do not have enough gas pressure at the meter, call the gas company. If you do have enough gas pressure at the meter but not at the water heater, check a different branch until you think you have the line singled out. Once you have the trouble line singled out, take it apart and see if it is clogged with dirt. Start at the dirt leg (or drip leg) of the water heater. If the water heater does not have a drip leg, more than likely debris has clogged the gas valve. Sometimes when a burner shuts off, it will make a loud pop, which indicates the line is dirty as well.

There will also be times where the gas pressure fluctuates. Most times this means two things: First, that there is water or moisture in the gas line. If you take the drip leg apart and water or moisture comes out, call the gas company or try and figure out why and how it is getting in. The second and more troublesome can be the “dust” that the gas company puts in their gas lines from the manufacturing plant. The gas company at times will manufacture the gas with drying agent (think white dust that is similar to the little silica bags that come in a pair of new shoes to dry out moisture). If your house is the unlucky house on the street that accumulates too much “dust,” it will clog the orifice in the burner, and send your W.C. readings dancing up and down.

The next installment of this series will cover testing thermocouples, piezos and pilot light issues.

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 22 years of experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College. 


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.