Almost nobody replaces a water heater on purpose. They replace it on a Saturday, in a hurry, standing in a wet basement, taking whatever can be got hold of the same day.
That is the expensive way to do it, and it is avoidable, because a tank almost always gives warning first. The signs just do not look like warnings.
The rumbling noise
A tank that pops, rumbles or bangs as it heats has sediment built up on the bottom. The burner is heating through a layer of it, water gets trapped underneath and flashes to steam, and the noise is that steam escaping through the sediment.
It is not immediately dangerous. What it is, is inefficient — you are paying to heat a layer of grit — and it is hard on the bottom of the tank, which is where a tank usually fails.
If yours has recently started making a noise it did not used to make, that is the earliest useful signal you will get.
Hot water that does not go as far as it used to
Same cause, different symptom. Sediment occupies volume that used to be water, so a tank that comfortably covered two showers now covers one and a half.
Worth ruling out the innocent explanations first: a new teenager in the house, a new shower head with a higher flow rate, or a dip tube problem. But a gradual, unexplained decline in how far the hot water goes is the classic middle-stage symptom.
Rusty or metallic hot water
If the hot runs discoloured and the cold does not, the discolouration is coming from inside the tank. That means the sacrificial anode rod — the part deliberately designed to corrode so the tank does not — has been used up, and the corrosion has moved on to the steel itself.
This one is significant. Once rust is coming out of the tank, the clock is genuinely running.
Damp at the base
Any moisture, rust streak or ring at the bottom of the tank should be treated as the final warning rather than a small problem to keep an eye on.
Tanks do not usually develop a slow, manageable drip and hold there. Once the steel is through, the pressure inside is doing the rest of the work, and what starts as damp becomes the full contents of the tank on the floor. Where that floor is a finished basement, the tank is the cheapest part of the day.
Do check first whether the water is actually coming from the tank rather than from a fitting above it or from the relief valve discharge — those are repairs, not replacements, and it is worth knowing which you are looking at.
What actually helps
- Drain a few gallons off the bottom once a year. It takes the sediment out before it builds into a layer. Most people never do this, and it is the single thing that most extends a tank's life.
- Have the anode rod checked when anybody is working on the system anyway. Replacing a used-up rod is a fraction of the cost of replacing a tank, and it is the whole reason the rod exists.
- Know where the shut-off is before you need it. The valve on the cold inlet at the top of the tank. Go and look at it now, and turn it to make sure it is not seized — the moment you actually need it is a bad time to find out that it is.
If it has already gone
Shut the water off at that valve, or at the main if it will not move. Kill the power to it — the breaker for an electric heater, the gas valve for a gas one. Then call.
And the honest part
Plenty of tanks that get replaced did not need to be. A pilot that will not stay lit, a failed thermocouple, a tripped high-limit switch or a burnt-out element are all repairs, and on a tank with life left in it a repair is the right answer.
If we look at yours and it is one of those, that is what we will tell you. Send a photo of the label and whatever it is doing, and quite often the conversation can start before anybody drives anywhere.