Urgent: water underneath the tank
A tank that is leaking from the tank itself does not heal, and it does not usually hold at a slow drip. The failure is corrosion working through the steel from the inside, and it enlarges.
Shut off the cold supply at the valve above the heater, turn the unit off — gas to pilot or the breaker off — and call. A 50-gallon tank is 50 gallons of water in the garage or, worse, in the hall.
Before assuming the worst, though, check where it is coming from. Not every puddle is a dead tank, and the difference is the difference between a small repair and a replacement.
- From the drain valve at the bottom. Often just a valve that needs tightening or replacing. Cheap.
- From the T&P relief valve, or its discharge pipe. Either a failed valve or — more importantly — the valve doing its job because pressure or temperature is too high. That needs investigating, not capping.
- From the inlet or outlet connections at the top. Fittings, usually repairable.
- From the body of the tank itself, or pooling with no visible source above it. That is the tank. It is not repairable.
Worth knowing
Never cap or plug a T&P discharge pipe to stop a drip. That valve is the safety device that stops a water heater becoming a pressure vessel. If it is discharging, something is asking it to — find out what.
Weeks, not months: rusty or discoloured hot water
If the rust appears only on the hot side, it is coming from inside the tank. Cold water running clear from the same tap confirms it is not the supply.
Every tank has a sacrificial anode rod — a metal rod that corrodes deliberately so the steel lining does not. It is doing its job right up until it is consumed. Once it is gone, the corrosion moves to the tank.
So rusty hot water is a sequenced warning: the anode is finished, the lining is now what is corroding, and the leak is the next event. On a heater under about eight years old, replacing the anode is worth doing and can add years. On an older tank, it is generally the tank telling you to plan.
The one thing not to do is ignore it. This is the sign that most reliably precedes the puddle.
Maintenance, not emergency: popping and rumbling
Sediment on the tank floor traps water underneath it. When the burner fires, that water flashes to steam and forces its way out through the layer — which is the popping you hear.
It means the layer is thick enough to insulate the burner, so you are losing efficiency and recovery speed, and the tank bottom is running hotter than designed. That shortens its life, but over years rather than days.
Flushing addresses it if it is caught reasonably early. On our water this is the argument for flushing annually rather than never — and the argument for a softener, which attacks the cause rather than the symptom.
Worth diagnosing: temperature and quantity problems
Running out of hot water sooner than you used to, or never getting it properly hot, is a capacity problem — and capacity is lost gradually to sediment, a failing element, or a broken dip tube. None of those will flood the house.
It is still worth acting on, because these are the symptoms that get much worse in winter when incoming water is colder and the heater has more work to do. Diagnosing in October is cheaper and less unpleasant than diagnosing in January.
There is a full walkthrough of the causes in why hot water gets worse every winter.
Age, and being honest about it
A conventional tank heater on our water is doing well to reach 10-12 years. The manufacturer's warranty is not a life expectancy, and hard water shortens both.
Once a tank is past about twelve, the calculation changes. Individual repairs are still cheap in isolation, but each one is being fitted to a vessel whose lining is corroding on a schedule nobody can see. Spending on a twelve-year-old tank frequently means paying twice.
We would rather tell you a heater is near the end than sell you a part for it. Equally, we will not condemn an eight-year-old tank that needs a thermocouple — that one is worth fixing, and we will say so.
Two things worth doing before winter
Lift the T&P valve's test lever briefly and let it snap back. Water should discharge and then stop cleanly. If nothing comes out, or it will not reseat, that valve needs attention — it is the one component whose failure is genuinely dangerous.
Then look underneath with a torch. Not for a puddle, which you would already have seen, but for rust streaks, mineral trails or a dried white crust down the side of the tank. Those are the marks left by a leak that evaporates between visits, and they are the earliest physical warning a tank gives.