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Question DetailsAsked on 2/17/2018

I just got home and heard my hot water tank running. Its brand new ( Nov. 2017) If no water was used all day why is

Been at work all day so no water was used. So why would it be running when I walked in?

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3 Answers


OK - does the water heater have water flowing through it, is it "firing" or heating water, or is the heat pump running ?

1) if water is actually flowing into it (should be able to clearly hear it if you put your ear to a water pipe, and the incoming water pipe will be quite cool or cold) then the water meter (if you have one) would be turning at least a bit, and you would have water coming out somewhere. if the heater has a problem, there would be water around the base of it or spraying out around the top somewhere, or water coming out of the drop pipe from the overpressure/overtemp valve at the top of the side of the tank.

If a hot water leak in the house, obviously watewr would be coming out at that leak.

If you don't know what water running in the pipes sounds like, listen at a faucet (obviously not a real hot one) with your ear to it, then turn the faucet on a bit and listen to what it sounds like with water running.

2) if the tank is heating - gas/oil burners are firing or electric elements are heating the water, which might make noise in the tank similar to water running, then it could just be the tank cooled off enough so the internal thermostat kicked it on to reheat the water. Commonly happens every half hour to hour with water heaters located outside or in unheated garage in cold weather, more like every hour to three or so for indoor heaters. Depending on make and model, this will commonly happen every time there is about a 10 to 20 degree drop in the water temperature - normally you would not notice it (one of those sounds you quickly tune out) but you may not have noticed it before or walked by just when it was firing.

3) if your heater has a heat pump on top - an electrical device on top with power cable to it, rather than just a flat top and a vent pipe and a couple of water pipes coming out, then that heat pump steals heat from the surrounding air to keep the water in the tank hot - even if water has not been used, can run from every 15 minutes or so to every hour or two, usually. Like in 2) above, this is just to keep the water in the tank hot so it is ready for use when you start using it. Typical regular and heat pump equipped water heaters look like this - regular one first, heat pump equipped one second:

Answered 2 years ago by LCD


Lost a couple of links I had appended, of similar questions with answers FYI:

Answered 2 years ago by LCD


OK - more than those two links got chopped from my original answer, and part of the answer got chopped off to, so continuing from the first response below:

In item 3) - here are what a normal and a heat-pump water heater look like - depending on whether normal or high-efficiency, may have metal "gravity flue" like one shown in first image of first article, or plastic "direct vent" flue pipe leading outside, with a damper and blower motor on it - but looks like shown at the top of the tank. Heat pump water heaters will have power cable/conduit to the heat pump on top, also.

4) if you have a direct-fired tankless water heater (produces hot water on demand), then periodically mosst of them run a heating cycle and eject some water to remove sediment and lime and such - sometimes based on a straight calendar timer (in case your unit is not being used because you are on a trip or such), sometimes at a certain interval since last firing cycle. So as far as you will see it, randomly firing for a short period of time.

5) if you have a combined hot water system - one boiler heating water both for domestic water and for a hydronic (hot water loop or baseboard) system, then if a zone thermostat calls for heat, it will start drawing water from the large combined water tank (commonly fiberglass) and as soon as it starts cooling down, the boiler will fire to reheat that. It also fires periodically to keep the water in the tank hot as it cools off, like in 2) and 3) above.

Answered 2 years ago by LCD

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