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Tankless Water Heater Making Noises? Here Are Some Possible Causes

Tankless Water Heater Making Noises? Here Are Some Possible Causes

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Tankless water heaters will all make some noise when starting up and heating water, but the noise levels are usually reasonable and not cause for concern. When the noise occurs when there is no hot water being used, it's likely there is a vacuum that's siphoning water away from the unit and causing loud noise and vibration. In most cases the solution is to have a plumber install a check valve in the water line to prevent other plumbing fixtures from interfering with the flow of water to the water heater.

Another common problem that can create noise in tankless water heaters is a dirty flow sensor which controls how much gas is sent to the unit. Other sources of noise include blocked or inadequate ventilation or a defective or improperly set pressure valve.

What Does a Bad Water Heater Sound Like?

  • Humming - If you are hearing humming noises, your water heater element is most likely loose, which makes the water flowing around it cause vibrations. These noises are not a cause for concern. A plumber can tighten the element when the humming bothers you. It is also possible for the home owner to tighten the element themselves if they are handy.
  • Hammering - Plumbers may call this "water hammering". When the pipes are mounted, they hit the wall, causing the noise. The pipes may not be securely anchored, and the water pressure can slam them against the studs or the interior of the wall. This can also be caused by abruptly turning on and off water, such as when flushing a toilet or operating a water pump without a holding tank for slowing down the flow of water. Although it is not a crucial issue, if you don't fix it you might end up with some damage later on. Water heater replacement is not necessary for this problem, since it has nothing to do with your water heater. That's not the source of the noise or the cause of the knocking. The problem can be resolved by having a plumber install a water hammer arrestor.
  • Hissing - Hissing sounds are often indicative of leaks. A water heater or a pipe leading to it will be the source of water or steam. The majority of the time, leaks of this type require the assistance of a professional plumber. Water heaters that are old may need to be replaced.
  • Screeching - A small opening is being pushed through under great pressure, causing those high pitched sounds. An incompletely opened valve usually causes this. You may find this valve at your water heater or closer to faucets or an appliance in your home. Determine where the noise is coming from by listening carefully. It may be necessary to replace the valve at the water heater itself. Make sure you're familiar with the process or have a professional plumber do it since the risk of steam burns is high.
  • Ticking - There is usually a tapping or ticking sound coming from heat traps or check valves that have been installed to encourage water to flow in the proper direction. Water heating and cooling in the pipes can also cause these types of sounds. Some homeowners are picky and will not tolerate the ticking or tapping noise, in which case you can replace the heat trap with a dielectric nipple. However, this does not guarantee the noises will stop. It is important to realize that this is not indicative of any real problem, so if you only hear it occasionally when you are in the room where your water heater is located, you would be best off ignoring it.


Because there can be many causes of the noise, it's best to have a plumber diagnose the problem and fix the unit if needed. Have questions about your water heater? Gibson's Heating & Plumbing, Inc. can help with all you hot water needs. Call us today!

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