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Not Enough Hot Water: Why It Runs Out Early

This is the more informative complaint of the two, because a heater that works briefly is telling you which half of it has failed.

Answer first

Hot water that starts fine and runs out early points at specific parts: a failed lower element on an electric heater, a broken dip tube sending cold water straight to the outlet, or sediment occupying the volume the tank was built to hold.

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On an electric heater, it is usually one element

An electric tank has two elements, upper and lower, and they do different jobs. The lower one does most of the heating; the upper one keeps the top of the tank hot. When the lower element fails you still get hot water — from the top of the tank only — and it runs out fast.

That symptom is close to diagnostic. A shower that starts hot and turns cold in a couple of minutes, on an electric heater, points at the lower element or its thermostat.

A broken dip tube

Cold water entering the tank is supposed to be carried to the bottom by a plastic dip tube, so it heats before it reaches the outlet. If the dip tube cracks or breaks off, incoming cold water mixes straight into the hot at the top, and the tank behaves as though it were half the size.

Sediment taking up the space

Minerals settle out of the water and build up in the bottom of the tank. That volume is no longer available for hot water, and on a gas heater the layer also insulates the water from the burner underneath it. A rumbling tank is the audible version of the same problem.

Or the tank is simply too small

If nothing has changed about the heater but the household has grown, the answer may be capacity rather than a fault. DOE puts a storage tank's life at 10 to 15 years, so a heater near that age with a growing household is often a replacement conversation rather than a repair one.

Source: US Department of Energy, Which Water Heater Is Right for You?.

Know the fuel and the symptom? That is most of the call.Gas and electric heaters fail in almost entirely different ways, so saying which you have gets you to the right person faster. We route the call and never charge you for it. Water heaters are what we write about; the number goes further.

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