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Question DetailsAsked on 5/1/2015

gas hot water heater outlet pipes humming, vibrating when water is used

it began with only hot water pipe humming then increased to both hot and cold pipes loudly humming.

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1 Answer


IF you mean as I read it - only the pipes right at the water heater are humming, then if you have a quite new electric water heater with the heat pump on it - looks something like this usually but the heat pump cann be a detached unit mounted near to and connected to the water heater itself - especially if less than about a uyear or two old and over 55 gallons (on top, blows cool air out of heat pump) then your heat pump is doing something funny - call right kind of contractor in your area - HVAC in probably most areas but plumbers in some. Ask when you call if they service that type unit. And turn off electric power till fixed to avoid further damage to unit. If gas like you say then likely does not have heat pump on it unless very high efficiency unit, which will have electric wiring to the heat pump if it has one. If so, turn off power to it till fixed.
Otherwise, listen for sounds of boiling in the heater - maybe you have not been draining it yearly. Else - likely (unless hum is coming from pipes contacting another sound source like a HVAC system) a partial blockage in the outlet pipe - many types have plastic fill tubes that direct the cold incoming water to the bottom of the tank, and they break up with heat and age and pieces can get blocked in the outlet pipe and have to be cleared out - maeans disconnecting the pipes and flushing out. One other rare but occasional cause - most houses that are not ancient have a tempering valve on the hot water pipe leading to the toilets so the tanks don't sweat when they fill with the cold water - it mixes hot water with the cold to the tank gets lukewarm water. Therefore, if the backflow check valves in it stick partly open or don't close, you can get crossflow between hot and cold water through it, causing a hum or howl or scream. Typically near the toilets, and may be separate ones for toilets a long ways apart in the house. Look like this typically - if making the noise listen at it with ear or a hollow tube to see if that is the source - would probably need a plumber to replace. Some types the valves can be replaced but if howling are probably eroded partly out, so just replace. hot and cold water are both connected to it (bottom in this case) and the single pipe coming out of it goes to the toilet fill valve. Should not be, but is sometimes installed in wall behind toilet, usually near hot water heater if that is near or underneath toilets. ========= IF sound occurs elsewhere in the house, not right at the water heater itself: Check first whether it occurs only when water is being used - if quiet the rest of the time, then the moving water in the pipers is causing it, so listen around the house - in air and with ear or stethoscope against pipes also - to track the source. Must be either a pump that turns on only when your water is on (booster or well pump), or a flow restriction causing turbulence that comes through as a humming - well pressure tank, water softener, restriction in hot water heater fill/draw tubes, malfunctioning or partly blocked or corroded pressure regulator or backflow preventer, etc.
Then if also occurs when water is not being used, check whether hot water heater is boiling - will hear it bubbling when it is in heating mode. Or furnace/boiler is firing or a HVAC fan or hydronic heating system pump is causing duct or heating system pipe vibration. Sump pumps can also do this, especially if stalled or running dry because float switch is not working right. More uncommon possibility is your household water pressure has increased so the water is running through the pipes to fast or forcefully so howls ONLY when the water is being used - would happen with hot and cold water use both unless regulator is only on the hot water heater (rare but sometimes is). Could be because utility cranked up the pressure, failed utility pump pressure switch so they are sending excess pressure through the mains, or failed pressure regulator in your house. Plumber can check, or you can buy a hose-threaded pressure gage for about $10 or less and connect to any hose-threaded faucet in your house EXCEPT ones on a steam or hot water heating system (whjich are low-pressure). Outdoors hose bib is usually easiest and least messy - make sure no other water is being used in the house when checking pressure. Should not be over about 60 psi ideally, over 75 is considered excessive, over 100 dangerous and likely to cause leaks. Here is also another prior similar queastion with more info on tracking down possible sources - All else fails, call Plumber.

Answered 5 years ago by LCD

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