A Leaking Water Heater: Which Leaks Wait and Which Do Not

Find where it is actually coming from

Water runs before it drips, so the wet patch is not the source. Dry everything, then look at three places in turn: the fittings at the top, the temperature and pressure relief valve on the side or top, and the base of the tank itself.

From a fitting

A weeping connection at the inlet or outlet is a repair, not a replacement. It is the best outcome on this page.

From the T&P relief valve

The temperature and pressure relief valve is a safety device: it opens if the tank goes over pressure or over temperature. A valve that discharges is sometimes faulty and is sometimes doing its job, which means something else is wrong — excess pressure, or a thermostat letting the water get far too hot.

Never plug, cap or block a T&P valve. It is the device that stops a water heater becoming a pressure vessel.

From the bottom of the tank itself

A tank leaking from its own shell is finished. The steel is glass-lined and once the lining fails the steel corrodes through; there is no patch. That is a replacement, and the reason it is urgent is that the failure gets worse rather than better.

Shut the cold supply off at the valve above the heater, and cut the power or gas to it, before deciding anything else.

Why it failed

Usually because the anode rod was used up years earlier and nobody replaced it. It is a consumable that protects the tank by corroding instead of it.