I installed a new water heater about 2 months ago and I hear this cracking noise most of the time, even when I have not used the hot water. Does anyone have an idea of what could possibly be causing that noise? I called the plumber who installed it but he refused to come to see it.


  • Where is it coming from? I keep asking myself.
    – Dan D.
    Apr 26, 2016 at 2:04
  • Could be air in the system, or perhaps loose rattling pipes, possibly aggravated by the installation. Apr 26, 2016 at 3:23

3 Answers 3


Keep in mind your water heater doesn't only run when you're using hot water. (assuming you have a regular tank-style unit, tankless are a very different beast) There's a number of things that COULD potentially be causing the noise but without more details it's gonna be impossible to say what. Unless you notice any other symptoms I wouldn't worry about it.

  • As @lowercaset mentioned, it's going to be difficult to troubleshoot without more information, but it is possible you're hearing the thermal expansion/contraction of the tank as the burner/element comes on or turns off.
    – bigbull15
    Apr 26, 2016 at 13:28

The most common cause of cracking noises associated with hot-water is the thermal expansion and contraction of metal pipes clamped against woodwork.

As the water in the tank cools, your heater will periodically come on and re-heat the water, even if you have not used any hot water. This thermal cycling can cause metal parts to heat up and expand. This can cause a range of sudden sounds from quiet clicking to louder cracking.

The only solutions I know of are to review the type, positioning and number of clamps used to hold the heater and any pipes from the heater to the taps/faucets.

I guess insulating the tank and pipes might help a little. I'd maybe try very-slightly loosening any pipe clamps and checking if the pipes run directly against woodwork anywhere.

It is also possible the cause of the sound is internal to the heater, in that case you can only wait and see if it gets better over time.


If you have a traditional gas heated tank heater; Sand and other debris can build up on the bottom and cause "bumping" . A steam bubble forms and as it rises off the bottom it collapses in the cooler water with a "thump" . The debris insulates the bottom so the steel gets above the boiling point . You can reduce the bumping by attaching a hose to the bottom drain and flushing the tank . I must do this frequently ( > twice/year) ; I have found that opening and closing the valve to the hose dislodges debris pretty good.

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