Tankless Water Heater Gas Smell Detection and Solutions

Oooppps!! That smell of gas next to your water heater or even from your backyard is not pretty normal. It’s okay to smell some combustible fumes when you turn it on and once your tankless water heater runs through its cycle; what’s not ordinary is the smell of fumes and even gas when the heater’s on and especially when it’s turned off.

You can readily associate this smell with your water heater and think that something’s not right. Why is this happening? I know that you have chosen your tankless water heater very carefully and you have eons of days just to compare all the pros and cons of the known brands. You’re already satisfied with your heater’s performance, but now you are in doubt that there is a gas leak because of that gas smell. Gas leak isn’t something to trifle with… of course, it can spell a huge trouble.

Why your tankless water heater smells like gas?

Before you panic, you can do something when you smell gas, you will have to put your pedal to the metal and get your replacement. Make sure to turn off the gas to your gas until it gets fixed.

To clarify this occurrence, let me first share to you the reasons of this gas smell. The general assumption is that the problem arises before the combustion and not the exhaust since combustion products are generally odorless. Nevertheless, this smell may happen primarily due to gas leak which may be because of the following:

1.The pin that pushes the gas valve which goes through the gland sleeve of the heater is gone. You can look at your heater’s gland sleeve and you will see calcium build up that is stuffed and you may also observe continuous water leak on that area – – this might be the source of the smelly gas.

2. Lack of maintenance and rust build up which cause the gas and water valve to corrode and leak.

3. Your water heater is old and worn out. As the unit ages, the functionality wears out and some of the part gets broken such as gas inlet and pilot tubes.

4. Inefficient water burning due to a poor venting. This can be dangerous because the burner emits carbon monoxide which can be poisonous. The natural level of CO2 is approximately 400ppm (.004% of air) and odourless, yet it can be smelly when mixed with other chemicals.

Where can your gas leak from?

Those gas leaks which produces that gas smell is quite serious and can be lethal. You must be cautious enough and should know where the leaking areas are. You can locate the gas leak on several areas of your tankless water heater and some of which are:

1.Your thermostat. If the leak is from your temperature control, this will require a full replacement

2. The reset button. This red reset button may have gas leak because the seal has been damaged

3. Under the dials. These dials are also the usual suspect for gas leaks and once your thermostat is replaced, these dials will also be changed.

4. Tubing nuts. These nuts from the connecting tube points or under your thermostat can also be a leakage area. You can only observe the leaks however when the unit is turned on.

5. Gas supply. The leak may not be from the water heater itself but from the flex line or connection that supply gas into it.

How can you detect if there’s really a gas leak? 

Detection is the initial solution to your suspicion. The first thing you must do is to check your tankless water heater carefully. Your water heater may function normally and will still give you good hot water but the smell will not go away; thus you must really examine the inside burner as well.  You must look for the general signs such as micro bubble cocoon or flames that appear.  You can inspect your water heater by following the simple steps below:

-If your carbon monoxide detector is going off a lot from the water heater, this can indicate a gas leak.

– Listen and check on any hissing noise near your water heater; although be very keen since you can mistake the sounds for boiling water being released under the sediment in the bottom of your water heater.

-Look inside your burner and watch out for blue popping flame even when the water is turned off. The popping blue flame indicates a gas leak. Some heater when turned on will give orange flames and this also indicates a leak. Bear in mind to use a flashlight, never a lighter or a candle when checking on your burners and don’t take cigarettes or cigars near them.

-If you can’t find any blue popping flames, you can create your soap and water solution that will be applied on the affected area. The mixture can be 1 table spoon dish soap and 1 cup of water. Combine the mixture on the container and gently swish or brush around making sure that the combination is thick and evenly distributed. Brush the mixture liberally to the suspected area on your water heater (the areas I discussed above are good options to look at).  If the bubbles appear on the pipe joints, there is probably a gas leak; but if it is leaking on the reset button, there’s a need to replace the valve.

-If you can’t still detect the gas leak using the soap and water mixture, you can buy a leak reactant, one example is the EZ FLO 45277 Hyrdo Balance Leak Seek which is a fluid spray and is more commonly known as the bluespray. Simply spray this reactant to the suspected areas and wait for bubbles to appear.

What to do when you confirm that there is a gas leak?

I assure you your hint is clear and that gas smell is not normal so what can you do? If you strongly believe that your water heater has gas leak, the first thing you must do is to turn off the water heater, the gas, and the water valves (located at the gas shut off valve portion connected to the water heater).

You can choose to fix your heater yourself. And try the steps below:

  • Tighten the nuts and bolts around the pilot light of the water heater. However, be careful not to tighten it too much that the compression fitting or farrel distorts.
  • You may also take the heater apart and check on the burner. If its rusty, you can clean it thoroughly using a vacuum.

A word of advice though: Do not to try to work with a connection to the gas line or the gas line yourself because it can lead to a more severe damage.

  • You must replace the vent or flue piping and regularly clean it. The water heater needs to be drained properly and debris must be removed. Tankless water heater can be vented in different ways such as concentric venting wherein the incoming and outgoing source of air can be combined thus forming a single pipe line.
  • If your heater still stinks after trying the two methods above, it’s time to call your contractor! He will better explain the occurrence to you. You can also call a professional plumber or your local fire department who can use sophisticated leak detectors and safely locate and repair the leak. If there’s a serious gas leak or an emergency, contact your energy company immediately.


You must not take for granted that gas smell since it can indicate a gas leak. A simple gas leak must not be assumed as a simple problem because this can lead to a major waste of money. Consider that your tankless water heater is in an enclosed space and a gas leak can lead to a major explosion risk. Installation of carbon monoxide alarms and regular service maintenance can also be good preventive measures and can save you a lot of money, time and even your lives.

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