Your water heater can make noise in a variety of ways ranging from hissing, popping, tapping, banging, and even jackhammer sounds. Some are indicators of problems while others are just age and improper maintenance that really are not much of a concern but will go away when the water heater is eventually replaced.
A hissing or, popping sound when the water heater is reheating is one of the more common sounds a water heater makes. When water is heated the water molecules expand taking up more room leaving less room for other things in the solution. The hardness minerals dissolved in the water such as lime feel this molecular expansion and precipitate out of the solution falling to the bottom of the water heater. The minerals build up on the bottom of the water heater and if you do not periodically flush the water heater will eventually coat the bottom of the water heater and may even cover the lower element in an electric water heater. This thick layer of minerals acts as insulation and keeps the water from having direct contact with the element of bottom of the tank. Water entrapped in the blanket of minerals being heated by the element on an electric water heater or, by the bottom of the tank on a gas water heater actually makes a series of small steam explosions as it is heated making hissing and popping sounds. If you have waited this long to flush your water heater the build up is probably quite hard and will not break up with just flushing. With gas water heaters the efficiency of the units will suffer, as the heat does not pass through the blanket of minerals as efficiently. With electric water heaters the build up covering the lower element will also affect heat transfer and many times will cause the element to overheat and burn out. With electric water heaters it is possible when changing a lower element to reach in through the hole for the lower element and break up the minerals so they may be flushed out.
A tapping noise or, buzzing noise when water is flowing can be caused by heat traps installed on the inlet and outlet of your water heater. Heat traps are basically small automatic valves that seal the inlet and outlet of the water heater when water is not flowing keeping the heat inside the insulated water heater instead of allowing the heat to escape into the pipes where it would be lost. Some manufacturers use heat traps that use a mechanism like a marble to seal the heat in. When water is flowing the “marble” moves in the flow making a tapping noise. Other manufacturers use heat traps, which have a flexible flapper type valve. This flexible flapper may vibrate at certain flow levels causing a buzzing sound when water is drawn. These sounds are generally harmless and will seem loudest at the inlet and outlet although the sound may transmit some distance away.
A banging noise when the water is shut off is usually water hammer. Water hammer is caused by the momentum of the water moving in the pipe coming to a sudden stop. The noise will often be a series of bangs louder at first and tapering off then stopping. Pipes that are not properly secured moving from the momentum can be a cause as well as excessive velocities of the flowing water in the pipes. Undersized pipes, and or, excessive pressure can cause the higher velocities. The pressure of your water supply should not exceed 80-psi and if it does a pressure-reducing valve should be installed in most cases with the pressure-reducing valve a thermal expansion tank should also be installed. Excessive velocities in a pipe may cause erosion of the pipe material resulting in leaks. Water hammer is a problem that may cause damage to components of your water supply system and should be addressed.
Jackhammer sounds are almost always accompanied by pulsations in the flow of water. This is usually caused by something loose in the stream of water, which in a sense is turning the water on and off rapidly making a constant series of water hammer type noises. These noises will often vary with the flow volume and may often disappear or, appear only within a certain flow range. Many times the loose debris may be a rubber washer on a valve that has come loose often from recent use. This is something that should be addressed as often it indicates a valve that will no longer function.
In any case while some noises may be harmless and not require any attention some may be serious and require repairs. For your safety it may be best to have a plumber check the noise out for you and determine its cause and if repairs are needed. Some noises particularly those relating to a gas burner operating on a water heater may be very serious and it is better to be safe than sorry.
I live in a duplex and both water heaters are on my side of the building. When my neighbor runs the shower or sink in the bathroom closest to us it sounds like a jet is taking off in our hall. Sometimes when they run the washer too. It seems to be only when they run the hot water. When they run the hot water in the far bathroom or kitchen it isn’t so bad.
And the noise is louder at night.
Sometimes I can hear a rattling sound right after they turn the hot water off. Sounds like the Heat Traps.
Any thoughts?
Hi Evan,
The jet taking off sounds like it could be a couple of things or, a combination of them.
High pressure will a higher velocity flow which can be quite noisy. The pressure is the first check I would make and it should read 80-psi or, less. Use a lazy hand gauge to record the pressure over a 24 hour period. If the water pressure is high they need to have a pressure reducing valve on the cold water line coming in and a thermal expansion tank on the water heater.
Undersized pipes lead to high velocity flows which can cause the noise. Also restrictions such as corroded galvanized pipes, or, partially closed valves can make noise. Corrosion at the water heater connections is common and may make noises.
The rattling sound when they turn the water off could be the heat traps or, it may also be sediment in the tank causing popping noises from the electrodes or, bottom of the water heater being covered insulating the heat from getting to the water causing little steam explosions.
Your neighbor has some things to have checked to determine the cause(s) of the noise.
Redwood
I have an 6 unit apartment which I have recently changed the community washer. Since about that time my tenants are experiencing a “fog horn” like noise throughout the building. It seems to be frequent, one person says it’s almost every hour. Could this be the valves for the hot/cold water supply to my washer?
Hi Bo,
Your thinking is good in terms of thinking of recent changes that may have caused problems, but in this case I’d suspect a toilet fill valve from a recent personal experience of my own. In our home we had a toilet fill valve go bad and start making the foghorn noise. That night someone used the toilet and my daughters dog (a beagle) ran baying through the house waking everyone up because of the unusual noise.
I would look at a toilet fill valve being the problem and perhaps because it seems like clockwork a leaking flapper as well causing the water level to leak down and refill. Probably an empty unit as no one has complained about happening whenever they flush their toilet. It wouldn’t hurt to ask the tenants though.
I would also recommend going through the entire building and replacing the flappers. Then doing it on a schedule as one leaking toilet can waste about 200 gallons a day which can bring you a massive water bill.
Redwood
I have a new State Ultra Low NOX gas water heater that makes a loud “foghorn” sound for at least a full minute after the burner lights, it appears there is a resonant frequency produced until the burner gets up to operating temperature. Any solutions?
Hi John,
Are you able to identify any specific area of the heater where the noise is coming from?
Redwood
Right at the air inlet surrounding the gas orifice, It’ even shaped like an air horn, an unusual looking arrangement!
It is on the SIDE of the tank, I might add!
Hi John,
I would recommend calling State to see what they say about the noise. 1-800-365-0024
Let me know what they say and how you make out with the noise.
Redwood
State sent me a service bulletin in .pdf form”Ultra Low Nox Service Bulletin Noises and Vibration” which basically says to remove the burner assembly and then to spread apart, or bend the two sheetmetal fingers (at the back of the combustion chamber area) that serve to locate and support the burner assembly under spring tension when it is in place. I did this and it did reduce the volume and the duration of the noise produced to a much more livable level.
Hi John,
I’m glad they had a TSB on it. I had checked their website when you originally posted but didn’t find one.
Redwood